shader: Unify shader stage types

src/shader_recompiler/stage.h

@@ -9,13 +9,20 @@
 namespace Shader {
 
 enum class Stage : u32 {
-    Compute,
-    VertexA,
     VertexB,
     TessellationControl,
     TessellationEval,
     Geometry,
     Fragment,
+
+    Compute,
+
+    VertexA,
 };
+constexpr u32 MaxStageTypes = 6;
+
+[[nodiscard]] constexpr Stage StageFromIndex(size_t index) noexcept {
+    return static_cast<Stage>(static_cast<size_t>(Stage::VertexB) + index);
+}
 
 } // namespace Shader