sem: Split sem::Variable into global, local and parameter

Each of these may contain information specific to their kind.

Change-Id: Ic8ac808088132b7bc2e43da6ce46a06571e0fed5
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/59200
Kokoro: Kokoro <noreply+kokoro@google.com>
Reviewed-by: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: James Price <jrprice@google.com>

src/sem/call_target.h

@@ -18,39 +18,15 @@
 #include <vector>
 
 #include "src/sem/node.h"
-#include "src/sem/parameter_usage.h"
 #include "src/sem/sampler_type.h"
+#include "src/sem/variable.h"
 #include "src/utils/hash.h"
 
 namespace tint {
-
 namespace sem {
 // Forward declarations
 class Type;
 
-/// Parameter describes a single parameter of a call target
-struct Parameter {
-  /// Parameter type
-  sem::Type* const type;
-  /// Parameter usage
-  ParameterUsage const usage = ParameterUsage::kNone;
-};
-
-std::ostream& operator<<(std::ostream& out, Parameter parameter);
-
-/// Equality operator for Parameters
-static inline bool operator==(const Parameter& a, const Parameter& b) {
-  return a.type == b.type && a.usage == b.usage;
-}
-
-/// Inequality operator for Parameters
-static inline bool operator!=(const Parameter& a, const Parameter& b) {
-  return !(a == b);
-}
-
-/// ParameterList is a list of Parameter
-using ParameterList = std::vector<Parameter>;
-
 /// @param parameters the list of parameters
 /// @param usage the parameter usage to find
 /// @returns the index of the parameter with the given usage, or -1 if no
@@ -85,19 +61,4 @@ class CallTarget : public Castable<CallTarget, Node> {
 }  // namespace sem
 }  // namespace tint
 
-namespace std {
-
-/// Custom std::hash specialization for tint::sem::Parameter
-template <>
-class hash<tint::sem::Parameter> {
- public:
-  /// @param p the tint::sem::Parameter to create a hash for
-  /// @return the hash value
-  inline std::size_t operator()(const tint::sem::Parameter& p) const {
-    return tint::utils::Hash(p.type, p.usage);
-  }
-};
-
-}  // namespace std
-
 #endif  // SRC_SEM_CALL_TARGET_H_