Metal: Implement suppot for clip plane toggling via GPU_clip_distances.

The Metal backend already supports output for the 6 clipping planes via gl_ClipDistances equivalent, however, functionality to toggle clipping plane enablement was missing.

Authored by Apple: Michael Parkin-White

Ref T96261
Depends on D16777

Reviewed By: fclem

Maniphest Tasks: T96261

Differential Revision: https://developer.blender.org/D16813

source/blender/gpu/metal/mtl_state.hh

@@ -80,6 +80,8 @@ class MTLStateManager : public StateManager {
   void mtl_depth_range(float near, float far);
   void mtl_stencil_mask(uint mask);
   void mtl_stencil_set_func(eGPUStencilTest stencil_func, int ref, uint mask);
+  void mtl_clip_plane_enable(uint i);
+  void mtl_clip_plane_disable(uint i);
 
   MEM_CXX_CLASS_ALLOC_FUNCS("MTLStateManager")
 };