[Fix] (MG_Impl): report the draw-indirect binding and the buffer access state

Three pieces of queryable buffer state were missing, all of them read by the
KHR-GL40.draw_indirect basic-binding-* and basic-buffer-* cases:

- GL_DRAW_INDIRECT_BUFFER_BINDING had no case in glGetIntegerv, so it raised
  GL_INVALID_ENUM and left the caller's variable untouched (the test read back its own
  -9999 sentinel). GL_DISPATCH_INDIRECT_BUFFER_BINDING right next to it was already
  handled; this is the same two lines against BufferTarget::DrawIndirect. Because
  glGetBooleanv/glGetFloatv/glGetDoublev all widen from the integer path, one case
  fixes all four getters.
- GL_BUFFER_ACCESS answered 0 for an unmapped buffer. Its initial value is
  GL_READ_WRITE and glUnmapBuffer restores it (GL 4.6 core table 6.2); 0 is not a legal
  value of that state at all, and the test threw on the unrecognised enum.
- GL_BUFFER_ACCESS_FLAGS was not implemented, so it fell through to the invalid-pname
  arm. It is the MapBufferRange bitfield verbatim, which the mapping access flags
  already hold in normalised form - glMapBuffer's access enum is converted on the way
  in - so it converts straight back out, and reads zero while unmapped.

MobileGL/MG_Impl/GLImpl/Buffer/GL_Buffer.cpp

@@ -330,12 +330,21 @@ namespace MobileGL::MG_Impl::GLImpl {
                     } else if (access & BufferMappingAccessBit::Write) {
                         *params = GL_WRITE_ONLY;
                     } else {
-                        *params = 0;
+                        *params = GL_READ_WRITE;
                     }
                 } else {
-                    *params = 0;
+                    // Initial value, and what glUnmapBuffer restores (GL 4.6 core table 6.2).
+                    *params = GL_READ_WRITE;
                 }
                 break;
+            case GL_BUFFER_ACCESS_FLAGS:
+                // The MapBufferRange flags verbatim; glMapBuffer's access enum has already been
+                // normalised into the same bits. Zero while the buffer is not mapped.
+                *params = bufferObject->IsMapped()
+                    ? static_cast<GLint>(
+                          MG_Util::ConvertBufferMappingAccessToGLEnum(bufferObject->GetMappingAccess()))
+                    : 0;
+                break;
             case GL_BUFFER_MAPPED:
                 *params = bufferObject->IsMapped() ? GL_TRUE : GL_FALSE;
                 break;

MobileGL/MG_Impl/GLImpl/Getter/GL_Getter.cpp

@@ -1030,6 +1030,11 @@ namespace MobileGL::MG_Impl::GLImpl {
             *params = obj ? static_cast<GLint>(obj->GetExternalIndex()) : 0;
             return;
         }
+        case GL_DRAW_INDIRECT_BUFFER_BINDING: {
+            auto& obj = MG_State::pGLContext->GetBufferBindingSlot(BufferTarget::DrawIndirect).GetBoundObject();
+            *params = obj ? static_cast<GLint>(obj->GetExternalIndex()) : 0;
+            return;
+        }
         case GL_MAX_DEBUG_GROUP_STACK_DEPTH:
             *params = 0; // debug-group entrypoints are stubbed
             return;

MobileGL/MG_Util/Converters/MGToGL/BufferEnumConverter.cpp

@@ -73,7 +73,7 @@ namespace MobileGL {
             }
         }
 
-        GLbitfield ConvertBufferMappingAccessToGLEnum(BufferMappingAccessBit access) {
+        GLbitfield ConvertBufferMappingAccessToGLEnum(Flags<BufferMappingAccessBit> access) {
             GLbitfield result = 0;
             if (access & BufferMappingAccessBit::Read) result |= GL_MAP_READ_BIT;
             if (access & BufferMappingAccessBit::Write) result |= GL_MAP_WRITE_BIT;

MobileGL/MG_Util/Converters/MGToGL/BufferEnumConverter.h

@@ -14,6 +14,6 @@ namespace MobileGL {
     namespace MG_Util {
         GLenum ConvertBufferTargetToGLEnum(BufferTarget bufferTarget);
         GLenum ConvertBufferUsageToGLEnum(BufferUsage usage);
-        GLbitfield ConvertBufferMappingAccessToGLEnum(BufferMappingAccessBit access);
+        GLbitfield ConvertBufferMappingAccessToGLEnum(Flags<BufferMappingAccessBit> access);
     } // namespace MG_Util
 } // namespace MobileGL