shader: Allow tracking of indirect buffers without variable offset

While changing this code, simplify tracking code to allow returning
the base address node, this way callers don't have to manually rebuild
it on each invocation.

src/video_core/shader/track.cpp

@@ -32,39 +32,44 @@ std::pair<Node, s64> FindOperation(const NodeBlock& code, s64 cursor,
     }
     return {};
 }
-} // namespace
+} // Anonymous namespace
 
-Node ShaderIR::TrackCbuf(Node tracked, const NodeBlock& code, s64 cursor) const {
+std::tuple<Node, u32, u32> ShaderIR::TrackCbuf(Node tracked, const NodeBlock& code,
+                                               s64 cursor) const {
     if (const auto cbuf = std::get_if<CbufNode>(&*tracked)) {
-        // Cbuf found, but it has to be immediate
-        return std::holds_alternative<ImmediateNode>(*cbuf->GetOffset()) ? tracked : nullptr;
+        // Constant buffer found, test if it's an immediate
+        const auto offset = cbuf->GetOffset();
+        if (const auto immediate = std::get_if<ImmediateNode>(&*offset)) {
+            return {tracked, cbuf->GetIndex(), immediate->GetValue()};
+        }
+        return {};
     }
     if (const auto gpr = std::get_if<GprNode>(&*tracked)) {
         if (gpr->GetIndex() == Tegra::Shader::Register::ZeroIndex) {
-            return nullptr;
+            return {};
         }
         // Reduce the cursor in one to avoid infinite loops when the instruction sets the same
         // register that it uses as operand
         const auto [source, new_cursor] = TrackRegister(gpr, code, cursor - 1);
         if (!source) {
-            return nullptr;
+            return {};
         }
         return TrackCbuf(source, code, new_cursor);
     }
     if (const auto operation = std::get_if<OperationNode>(&*tracked)) {
         for (std::size_t i = 0; i < operation->GetOperandsCount(); ++i) {
-            if (const auto found = TrackCbuf((*operation)[i], code, cursor)) {
-                // Cbuf found in operand
+            if (auto found = TrackCbuf((*operation)[i], code, cursor); std::get<0>(found)) {
+                // Cbuf found in operand.
                 return found;
             }
         }
-        return nullptr;
+        return {};
     }
     if (const auto conditional = std::get_if<ConditionalNode>(&*tracked)) {
         const auto& conditional_code = conditional->GetCode();
         return TrackCbuf(tracked, conditional_code, static_cast<s64>(conditional_code.size()));
     }
-    return nullptr;
+    return {};
 }
 
 std::optional<u32> ShaderIR::TrackImmediate(Node tracked, const NodeBlock& code, s64 cursor) const {