Shader_IR: add the ability to amend code in the shader ir.

This commit introduces a mechanism by which shader IR code can be
amended and extended. This useful for track algorithms where certain
information can derived from before the track such as indexes to array
samplers.

src/video_core/shader/node.h

@@ -392,8 +392,30 @@ struct MetaImage {
 using Meta =
     std::variant<MetaArithmetic, MetaTexture, MetaImage, MetaStackClass, Tegra::Shader::HalfType>;
 
+class AmendNode {
+public:
+    std::optional<u32> GetAmendIndex() const {
+        if (amend_index == amend_null_index) {
+            return std::nullopt;
+        }
+        return {amend_index};
+    }
+
+    void SetAmendIndex(u32 index) {
+        amend_index = index;
+    }
+
+    void ClearAmend() {
+        amend_index = amend_null_index;
+    }
+
+private:
+    static constexpr u32 amend_null_index = 0xFFFFFFFF;
+    u32 amend_index{amend_null_index};
+};
+
 /// Holds any kind of operation that can be done in the IR
-class OperationNode final {
+class OperationNode final : public AmendNode {
 public:
     explicit OperationNode(OperationCode code) : OperationNode(code, Meta{}) {}
 
@@ -433,7 +455,7 @@ private:
 };
 
 /// Encloses inside any kind of node that returns a boolean conditionally-executed code
-class ConditionalNode final {
+class ConditionalNode final : public AmendNode {
 public:
     explicit ConditionalNode(Node condition, std::vector<Node>&& code)
         : condition{std::move(condition)}, code{std::move(code)} {}
@@ -630,7 +652,7 @@ private:
 };
 
 /// Commentary, can be dropped
-class CommentNode final {
+class CommentNode final : public AmendNode {
 public:
     explicit CommentNode(std::string text) : text{std::move(text)} {}