Implement static name resolution (#958)

This doesn't actually use the results of name resolution, but it does verify that they are present.
Also ensures that name resolution and type checking are applied to deduced function parameters and the implicit call to `Main()`.

Co-authored-by: Jon Meow <46229924+jonmeow@users.noreply.github.com>

executable_semantics/ast/ast.h

@@ -26,6 +26,8 @@ struct AST {
   std::vector<Nonnull<Declaration*>> declarations;
   // Names declared at the top level of the file.
   StaticScope static_scope;
+  // Synthesized call to `Main`. Injected after parsing.
+  std::optional<Nonnull<CallExpression*>> main_call;
 };
 
 }  // namespace Carbon