[Perf] (MG_Backend/DirectGLES, MG_Impl): cache link-time lookups, bound unit scans, honor eglSwapInterval

- BackendProgramObjectImpl::CacheResourceLocations resolves every
  glGetUniformBlockIndex / glGetUniformLocation string query once per
  link and establishes the block binding points there. Per draw,
  BindCurrentProgramWithResources now uses the cached indices, re-issues
  glUniform1i only when a sampler's unit actually changed (program state
  persists), uploads the global UBO only when its content version moved,
  and skips redundant glUseProgram binds (guard reset on program-name
  reuse, MakeCurrent, and every explicit glUseProgram(0)). The caches are
  invalidated through ProgramObject's link version, which also makes a
  relinked program finally re-sync its backend program.
- Track a texture-unit high-water mark (fed by glBindTexture /
  glBindTextureUnit / glBindSampler / glBindImageTexture) so the two
  per-draw unit scans (MAX_TEXTURE_IMAGE_UNITS is 192) and the
  texture-deletion unbind loop only walk units that were ever touched.
- Forward the app's eglSwapInterval to the native EGL surface through a
  new BackendObject::SetEGLSwapInterval hook (applied immediately when
  the surface exists, otherwise deferred to surface creation /
  MakeCurrent). "VSync off" finally reaches the hardware - DirectGLES
  was hard-locked to the display refresh before.

The driver-side cost of the per-draw string lookups was about half of a
30% Adreno driver hotspot; libMobileGL's share of the vanilla render
thread fell from 22% to 9% (simpleperf, Adreno 830).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

MobileGL/MG_Backend/BackendObject.h

@@ -175,6 +175,9 @@ namespace MobileGL {
         struct GlobalBackendFunctionsTable {
             GLFunctionsTable GL;
             void (*Present)();
+            // Optional: applies the app-requested eglSwapInterval to the native
+            // presentation path (null = backend keeps its own pacing policy).
+            void (*SetSwapInterval)(Int interval);
         };
 
         struct DynamicBackendParameters {
@@ -264,6 +267,9 @@ namespace MobileGL {
             virtual Bool CreateEGLPbufferSurface(EGLSurface surface, EGLint width, EGLint height);
             virtual Bool MakeEGLCurrent(EGLDisplay dpy, EGLSurface draw, EGLSurface read, EGLContext ctx);
             virtual Bool SwapEGLBuffers(EGLDisplay dpy, EGLSurface draw);
+            // Forwards the app-requested eglSwapInterval to the backend's native
+            // presentation path (no-op for backends without a SetSwapInterval hook).
+            virtual void SetEGLSwapInterval(Int interval);
             virtual void ReleaseEGLSurface(EGLSurface surface);
             virtual void ReleaseEGLResources();