Add semantic::Variable, use it.

Pull the mutable semantic field from ast::Variable and into a new semantic::Variable node.
Have the TypeDeterminer create these semantic::Variable nodes.

Bug: tint:390
Change-Id: Ia13f5e7b065941ed66ea5a86c6ccb288071feff3
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/40063
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: David Neto <dneto@google.com>

src/transform/emit_vertex_point_size.cc

@@ -58,7 +58,6 @@ Transform::Output EmitVertexPointSize::Run(const Program* in) {
       false,                                  // is_const
       nullptr,                                // constructor
       ast::VariableDecorationList{
-          // decorations
           out.create<ast::BuiltinDecoration>(Source{},
                                              ast::Builtin::kPointSize),
       });

src/transform/first_index_offset.cc

@@ -70,7 +70,7 @@ ast::Variable* clone_variable_with_new_name(CloneContext* ctx,
   return ctx->dst->create<ast::Variable>(
       ctx->Clone(in->source()),                // source
       ctx->dst->Symbols().Register(new_name),  // symbol
-      in->storage_class(),                     // storage_class
+      in->declared_storage_class(),            // declared_storage_class
       ctx->Clone(in->type()),                  // type
       in->is_const(),                          // is_const
       ctx->Clone(in->constructor()),           // constructor
@@ -226,7 +226,7 @@ ast::Variable* FirstIndexOffset::AddUniformBuffer(ProgramBuilder* dst) {
       ast::VariableDecorationList{
           dst->create<ast::BindingDecoration>(Source{}, binding_),
           dst->create<ast::GroupDecoration>(Source{}, group_),
-      });  // decorations
+      });
 
   dst->AST().AddGlobalVariable(idx_var);
 

src/transform/vertex_pulling.cc

@@ -35,6 +35,7 @@
 #include "src/clone_context.h"
 #include "src/program.h"
 #include "src/program_builder.h"
+#include "src/semantic/variable.h"
 #include "src/type/array_type.h"
 #include "src/type/f32_type.h"
 #include "src/type/i32_type.h"
@@ -150,7 +151,8 @@ void VertexPulling::State::FindOrInsertVertexIndexIfUsed() {
 
   // Look for an existing vertex index builtin
   for (auto* v : ctx.src->AST().GlobalVariables()) {
-    if (v->storage_class() != ast::StorageClass::kInput) {
+    auto* sem = ctx.src->Sem().Get(v);
+    if (sem->StorageClass() != ast::StorageClass::kInput) {
       continue;
     }
 
@@ -196,7 +198,8 @@ void VertexPulling::State::FindOrInsertInstanceIndexIfUsed() {
 
   // Look for an existing instance index builtin
   for (auto* v : ctx.src->AST().GlobalVariables()) {
-    if (v->storage_class() != ast::StorageClass::kInput) {
+    auto* sem = ctx.src->Sem().Get(v);
+    if (sem->StorageClass() != ast::StorageClass::kInput) {
       continue;
     }
 
@@ -229,7 +232,8 @@ void VertexPulling::State::FindOrInsertInstanceIndexIfUsed() {
 
 void VertexPulling::State::ConvertVertexInputVariablesToPrivate() {
   for (auto* v : ctx.src->AST().GlobalVariables()) {
-    if (v->storage_class() != ast::StorageClass::kInput) {
+    auto* sem = ctx.src->Sem().Get(v);
+    if (sem->StorageClass() != ast::StorageClass::kInput) {
       continue;
     }