[Feat] (Espryt): give the backend a dense {slot, gen} twin table beside the address-keyed registry

- SlotTables.h: BackendSlotTable<StateObject, BackendObject, kKind>, indexed by
  MGPipeHandle::Slot and validated by Gen, with the handle minted by the client
  MGPipeSlotAllocator off the frontend object GetLifetimeId(). A lookup is one bounds
  check plus one array index, and unlike the registry Find it never mutates the table,
  so a returned BackendPtr* is not invalidated by the next call on it.
- StateBackendObjectRegistry keeps its name, its signature and all ~40 call sites, and
  becomes the two-arm facade ARCHITECTURE.md 9.6 asks for: the pre-handle map under
  MOBILEGL_PIPE_LEGACY_MEMOS, the slot table under MOBILEGL_PIPE_PUSH, chosen once per
  process by EsprytSlotTablesEnabled() off kMGPipeSubsystemEsprytSlots. A clear bit with
  MOBILEGL_PIPE_LEGACY_MEMOS=0 leaves no arm at all and is Fatal{PipeLegacyMemosDisabled}.
- The kind is a template parameter only in the push build (MGB_TWIN_KIND_ARG): a third
  template argument would rename every instantiation and G1 wants the pull build byte
  identical. Pull-build symbol report is 0 added / 0 removed / 0 renamed and adds no
  resize beyond the three RenderState symbols the contract commit already moved.
- ForEachLive replaces begin()/end() under push and hands the callee a strong reference
  to the state object instead of the map key, which was the raw frontend address.
- Nothing switches over yet: the tables are built and reachable, and the twins still go
  through whichever arm the bit selects.

MobileGL/MG_Backend/DirectGLES/Managers.cpp

@@ -170,6 +170,37 @@ namespace MobileGL::MG_Backend::DirectGLES {
                        [] { std::atexit(+[] { g_processTeardown = true; }); });
     }
 
+#if MOBILEGL_PIPE_PUSH
+    Bool EsprytSlotTablesEnabled() {
+        // Latched once, not read per call: the two arms of StateBackendObjectRegistry keep
+        // their twins in different containers, so an answer that changed mid-run would strand
+        // every twin already built (and, for the driver ids those twins own, leak them).
+        static const Bool enabled = [] {
+            const Bool bitSet =
+                (MG_Config::Features.PipePush & MG_Pipe::kMGPipeSubsystemEsprytSlots) != 0;
+#if MOBILEGL_PIPE_LEGACY_MEMOS
+            if (!bitSet && !MG_Config::Features.PipeLegacyMemos) {
+                // The operator asked for the handle arm to be OFF and the legacy arm to be
+                // unreachable at the same time, which leaves no arm at all. Say so at startup
+                // rather than silently running the thing they turned off (ARCHITECTURE.md 9.6).
+                MGLOG_F("MGPipe: Fatal{PipeLegacyMemosDisabled, \"kMGPipeSubsystemEsprytSlots "
+                        "is clear but MOBILEGL_PIPE_LEGACY_MEMOS=0\"}");
+            }
+            return bitSet;
+#else
+            // The legacy arm is not compiled, so the handle arm is the only arm. The bit still
+            // decides nothing here; it is recorded so a log reader sees the mismatch.
+            if (!bitSet) {
+                MGLOG_D("MGPipe: kMGPipeSubsystemEsprytSlots is clear but this build has no "
+                        "legacy twin registry; running the handle arm anyway");
+            }
+            return true;
+#endif
+        }();
+        return enabled;
+    }
+#endif
+
     Bool VertexStageStorageBlockUsable(Int maxVertexShaderStorageBlocks) {
         // One block is all the indirect-params view needs, so this is a >= 1 test and not a
         // budget calculation. Negative is treated as unusable rather than clamped: a driver
@@ -2744,7 +2775,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
             return true;
         }
 
-        StateBackendObjectRegistry<MG_State::GLState::VertexArrayObject, BackendVertexArrayObject>
+        StateBackendObjectRegistry<MG_State::GLState::VertexArrayObject, BackendVertexArrayObject MGB_TWIN_KIND_ARG(MG_Pipe::MGPipeKind::VertexElementsCso)>
             g_backendVertexArrayObjects;
     } // namespace VertexArrayImpl
 
@@ -5072,7 +5103,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
         Array<Array<BackendTextureObject*, (SizeT)TextureTarget::TextureTargetCount>,
               MG_State::GLState::TextureState::MAX_TEXTURE_IMAGE_UNITS>
             g_boundTexturesCache;
-        StateBackendObjectRegistry<MG_State::GLState::ITextureObject, BackendTextureObject> g_backendTextureObjects;
+        StateBackendObjectRegistry<MG_State::GLState::ITextureObject, BackendTextureObject MGB_TWIN_KIND_ARG(MG_Pipe::MGPipeKind::Texture)> g_backendTextureObjects;
     } // namespace TextureImpl
 
     namespace FramebufferImpl {
@@ -5825,7 +5856,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
             return m_backendColorSlots[index];
         }
 
-        StateBackendObjectRegistry<MG_State::GLState::FramebufferObject, BackendFramebufferObject>
+        StateBackendObjectRegistry<MG_State::GLState::FramebufferObject, BackendFramebufferObject MGB_TWIN_KIND_ARG(MG_Pipe::MGPipeKind::Framebuffer)>
             g_backendFramebufferObjects;
         Array<Uint16, SizeT(FramebufferTarget::FramebufferTargetCount)> g_fboSyncedSlotVersions = {0};
         // Tracks the bound FBO's object version (bumped on any attachment/drawbuffer change)
@@ -6136,7 +6167,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
         // context never answers GL_NO_ERROR, and the build runs on the thread that would
         // then spin forever.
         constexpr Int kMaxDrainedProgramErrors = 32;
-        StateBackendObjectRegistry<MG_State::GLState::ProgramObject, BackendProgramObjectImpl> g_backendProgramObjects;
+        StateBackendObjectRegistry<MG_State::GLState::ProgramObject, BackendProgramObjectImpl MGB_TWIN_KIND_ARG(MG_Pipe::MGPipeKind::ShaderCso)> g_backendProgramObjects;
 
         BackendProgramObjectImpl::BackendProgramObjectImpl() {
 #ifdef TRACY_ENABLE
@@ -8654,7 +8685,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
         }
 
         Array<BackendSamplerObject*, MG_State::GLState::TextureState::MAX_TEXTURE_IMAGE_UNITS> g_boundSamplersCache;
-        StateBackendObjectRegistry<MG_State::GLState::SamplerObject, BackendSamplerObject> g_backendSamplerObjects;
+        StateBackendObjectRegistry<MG_State::GLState::SamplerObject, BackendSamplerObject MGB_TWIN_KIND_ARG(MG_Pipe::MGPipeKind::SamplerCso)> g_backendSamplerObjects;
     } // namespace SamplerImpl
 
     namespace RenderbufferImpl {
@@ -8766,7 +8797,7 @@ namespace MobileGL::MG_Backend::DirectGLES {
             MGLOG_D("RBO %u sync completed. backend ID %u", stateRBOObject->GetExternalIndex(), m_backendRBOId);
         }
 
-        StateBackendObjectRegistry<MG_State::GLState::RenderbufferObject, BackendRenderbufferObject>
+        StateBackendObjectRegistry<MG_State::GLState::RenderbufferObject, BackendRenderbufferObject MGB_TWIN_KIND_ARG(MG_Pipe::MGPipeKind::Renderbuffer)>
             g_backendRenderbufferObjects;
     } // namespace RenderbufferImpl
 } // namespace MobileGL::MG_Backend::DirectGLES