shader: run merged geometry stages as mesh shaders

Co-authored-by: Brandon Strong <brandostrong@gmail.com>
Co-authored-by: fxpw <fxpw@outlook.com>
Co-authored-by: shadowbeat070 <70843316+shadowbeat070@users.noreply.github.com>

src/graphics/shader/recompiler/backend/spirv/spirvEmitterAnalysis.cpp

@@ -278,6 +278,7 @@ void EmitStorageImageWrite(EmitterState& state, uint32_t resource, uint32_t mip_
 uint32_t ExecutionModelForStage(ShaderType stage) {
 	switch (stage) {
 		case ShaderType::Vertex: return ExecutionModelVertex;
+		case ShaderType::Mesh: return 5365u; // MeshEXT
 		case ShaderType::Pixel: return ExecutionModelFragment;
 		default: return ExecutionModelGLCompute;
 	}