[Feat] (MG_State, MG_Impl/GLImpl): per-target default texture objects (name 0) - binding 0 binds a real per-context default object (the initial binding of every unit/target slot, rebound on delete of a bound texture), so glTexImage*/glTexParameter*/glGetTex* on it work like any texture while glIsTexture(0)/Gen/Delete keep excluding it and TexStorage* rejects it per spec; backends skip image-less defaults as cheaply as the old null slots (DirectGLES per-draw sync/bind loops, DirectVulkan sampler-fallback resolve); also accept the full advertised GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS range in glActiveTexture, allow zero-layer TexImage3DMultisample, and let glTexBuffer(buffer=0) detach - the texture section of GL CTS per-case state reset (gluStateReset) now runs clean

MobileGL/MG_State/GLState/Core.cpp

@@ -226,6 +226,10 @@ namespace MobileGL::MG_State {
             return m_textureState.GetTextureObject(index);
         }
 
+        const SharedPtr<ITextureObject>& GLContext::GetDefaultTextureObject(TextureTarget target) const {
+            return m_textureState.GetDefaultTextureObject(target);
+        }
+
         const SharedPtr<ITextureObject>& GLContext::CreateTextureObject(Uint index, TextureTarget target) {
             return m_textureState.CreateTextureObject(index, target);
         }