Reduce duplicate GPU buffer uploads (#3577)

Co-authored-by: “Malcolm <“mtoon@atlasprogramming.com”>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

include/mbgl/mtl/render_pass.hpp

@@ -41,6 +41,9 @@ public:
     /// Set the sampler for a texture binding
     void setFragmentSamplerState(const MTLSamplerStatePtr&, int32_t location);
 
+    /// Set the render pipeline state
+    void setRenderPipelineState(const MTLRenderPipelineStatePtr&);
+
     void endEncoding();
 
     /// Resets the states and bindings of the render pass to deal
@@ -69,6 +72,8 @@ private:
     mtl::CommandEncoder& commandEncoder;
     MTLRenderCommandEncoderPtr encoder;
     MTLDepthStencilStatePtr currentDepthStencilState;
+    MTLRenderPipelineStatePtr currentPipelineState;
+
     int32_t currentStencilReferenceValue = 0;
     std::vector<gfx::DebugGroup<gfx::RenderPass>> debugGroups;