Merge #1735

1735: macro: Allow builtin `MacroInvocation`s within the AST r=CohenArthur a=CohenArthur

gcc/rust/ChangeLog:

	* ast/rust-macro.h (enum class): Add `BuiltinMacro` enum class
	* expand/rust-attribute-visitor.cc (AttrVisitor::visit): Mention switching on `macro.kind` once builtin macro invocations are properly handled
	* parse/rust-parse-impl.h (Parser::parse_macro_invocation): Switch to new MacroInvocation API
	(Parser::parse_type): Switch to new MacroInvocation API
	(Parser::parse_type_no_bounds): Switch to new MacroInvocation API

This will be necessary for proper handling of builtin macros with the new `EarlyNameResolver` class and associated fixed-point algorithm

Co-authored-by: Arthur Cohen <arthur.cohen@embecosm.com>