gccrs: builtins: Rename all bang macro handlers

gcc/rust/ChangeLog:

	* expand/rust-macro-builtins.cc (MacroBuiltin::assert): Rename to...
	(MacroBuiltin::assert_handler): ..this.
	(MacroBuiltin::file): Rename to...
	(MacroBuiltin::file_handler): ..this.
	(MacroBuiltin::column): Rename to...
	(MacroBuiltin::column_handler): ..this.
	(MacroBuiltin::include_bytes): Rename to...
	(MacroBuiltin::include_bytes_handler): ..this.
	(MacroBuiltin::include_str): Rename to...
	(MacroBuiltin::include_str_handler): ..this.
	(MacroBuiltin::compile_error): Rename to...
	(MacroBuiltin::compile_error_handler): ..this.
	(MacroBuiltin::concat): Rename to...
	(MacroBuiltin::concat_handler): ..this.
	(MacroBuiltin::env): Rename to...
	(MacroBuiltin::env_handler): ..this.
	(MacroBuiltin::cfg): Rename to...
	(MacroBuiltin::cfg_handler): ..this.
	(MacroBuiltin::include): Rename to...
	(MacroBuiltin::include_handler): ..this.
	(MacroBuiltin::line): Rename to...
	(MacroBuiltin::line_handler): ..this.
	* expand/rust-macro-builtins.h: Rename all handlers.
	* util/rust-hir-map.cc (Mappings::insert_macro_def): Use new handler
	names.