### Godot version

4.1.1

### System information

Meta Quest 2 - GLES3

### Issue description

When writing VR applications on Godot 4 using gl_compatibility, skeleton-driven meshes like hands are often rendered corrupted, or sometimes update slowly.

### Steps to reproduce

The godot-xr-tools demo projects have these issues in the climbing/gliding and pointer-demo scenes if the project is switched to gl_compatibility mode and run on a mobile VR headset.

### Minimal reproduction project

The godot-xr-tools demo project has been the testing project for this issue.
}
void MeshStorage::update_mesh_instances() {
	if (dirty_mesh_instance_arrays.first() == nullptr) {
		return; 
	}
	glEnable(GL_RASTERIZER_DISCARD);
	
	while (dirty_mesh_instance_arrays.first()) {
		MeshInstance *mi = dirty_mesh_instance_arrays.first()->self();
		Skeleton *sk = skeleton_owner.get_or_null(mi->skeleton);
		
		float base_weight = 1.0;
		if (mi->mesh->blend_shape_count && mi->mesh->blend_shape_mode == RS::BLEND_SHAPE_MODE_NORMALIZED) {
			for (uint32_t i = 0; i < mi->mesh->blend_shape_count; i++) {
				base_weight -= mi->blend_weights[i];
			}
		}
		for (uint32_t i = 0; i < mi->surfaces.size(); i++) {
			if (mi->surfaces[i].vertex_buffer == 0 || mi->mesh->surfaces[i]->skeleton_vertex_array == 0) {
				continue;
			}
			bool array_is_2d = mi->surfaces[i].format_cache & RS::ARRAY_FLAG_USE_2D_VERTICES;
			bool can_use_skeleton = sk != nullptr && sk->use_2d == array_is_2d && (mi->surfaces[i].format_cache & RS::ARRAY_FORMAT_BONES);
			bool use_8_weights = mi->surfaces[i].format_cache & RS::ARRAY_FLAG_USE_8_BONE_WEIGHTS;
			
			if (mi->mesh->blend_shape_count) {
				SkeletonShaderGLES3::ShaderVariant variant = SkeletonShaderGLES3::MODE_BASE_PASS;
				uint64_t specialization = 0;
				specialization |= array_is_2d ? SkeletonShaderGLES3::MODE_2D : 0;
				specialization |= SkeletonShaderGLES3::USE_BLEND_SHAPES;