inspector: Implement a custom StageVariable copy constructor

The fields `has_location_decoration` and `location_decoration` are references to `has_location_attribute` and `location_attribute`, respectively, which act as an alias for a field-rename.

The default copy-constructor was copying across the reference (pointer) to the source StageVariable, instead of making a reference to the target's fields. This is causing Bad Things™ to happen in downstream projects.

Credit to dneto@ for identifying the issue, and for making this fix (which I've stolen for this CL).

Change-Id: Id0570e4e389f28980fa5aea29ad63b5100373dc5
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/79200
Reviewed-by: David Neto <dneto@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>

src/inspector/entry_point.cc

@@ -18,7 +18,17 @@ namespace tint {
 namespace inspector {
 
 StageVariable::StageVariable() = default;
-StageVariable::StageVariable(const StageVariable&) = default;
+StageVariable::StageVariable(const StageVariable& other)
+    : name(other.name),
+      has_location_attribute(other.has_location_attribute),
+      location_attribute(other.location_attribute),
+      has_location_decoration(has_location_attribute),
+      location_decoration(location_attribute),
+      component_type(other.component_type),
+      composition_type(other.composition_type),
+      interpolation_type(other.interpolation_type),
+      interpolation_sampling(other.interpolation_sampling) {}
+
 StageVariable::~StageVariable() = default;
 
 EntryPoint::EntryPoint() = default;

src/inspector/entry_point.h

@@ -59,7 +59,8 @@ struct StageVariable {
   /// Constructor
   StageVariable();
   /// Copy constructor
-  StageVariable(const StageVariable&);
+  /// @param other the StageVariable to copy
+  StageVariable(const StageVariable& other);
   /// Destructor
   ~StageVariable();