Update namer to use symbol table.

This Cl updates the various namer objects to work off the symbol table
instead of names.

Change-Id: I94b00a10225d0587f037cfaa6d9b42e2a8885734
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/35101
Reviewed-by: Ben Clayton <bclayton@google.com>
Commit-Queue: dan sinclair <dsinclair@chromium.org>
Auto-Submit: dan sinclair <dsinclair@chromium.org>

src/ast/module.cc

@@ -81,6 +81,10 @@ Symbol Module::RegisterSymbol(const std::string& name) {
   return symbol_table_.Register(name);
 }
 
+std::string Module::SymbolToName(const Symbol sym) const {
+  return symbol_table_.NameFor(sym);
+}
+
 bool Module::IsValid() const {
   for (auto* var : global_variables_) {
     if (var == nullptr || !var->IsValid()) {

src/ast/module.h

@@ -169,6 +169,11 @@ class Module {
   /// previously generated symbol will be returned.
   Symbol RegisterSymbol(const std::string& name);
 
+  /// Returns the `name` for `sym`
+  /// @param sym the symbol to retrieve the name for
+  /// @returns the use provided `name` for the symbol or "" if not found
+  std::string SymbolToName(const Symbol sym) const;
+
  private:
   Module(const Module&) = delete;