gccrs: Implement declarative macro 2.0 parser

gccrs: Implement declarative macro 2.0 parser

gcc/rust/ChangeLog:

	* ast/rust-ast-full-decls.h (class MacroItem): Remove forward declaration.
	* ast/rust-ast-full-test.cc (MacroRulesDefinition):
	Rework MacroRulesDefinition class
	* ast/rust-ast.h (class MacroItem): Remove abstract class.
	* ast/rust-item.h (class MacroItem): Remove forward declaration.
	* ast/rust-macro.h (class MacroItem): Likewise.
	(class MacroRulesDefinition): Add MacroKind enum.
	(class MacroInvocation): Fix inheritance.
	* lex/rust-token.h: Token "macro" is now used.
	* parse/rust-parse-impl.h (Parser::parse_item): Add handling for MACRO.
	(Parser::parse_vis_item): Call into parse_decl_macro_def.
	(Parser::parse_macro_item): Delete function.
	(Parser::parse_macro_rules_def): Return MBE macros only.
	(Parser::parse_decl_macro_def): New function.
	(Parser::parse_stmt): Handle MACRO token.
	(Parser::parse_stmt_or_expr_without_block): Call into parse_macro_rules_def.
	* parse/rust-parse.h: Declare new function.

gcc/testsuite/ChangeLog:

	* rust/compile/decl_macro1.rs: New test.
	* rust/compile/decl_macro2.rs: New test.
	* rust/compile/decl_macro3.rs: New test.
	* rust/compile/decl_macro4.rs: New test.
	* rust/compile/decl_macro5.rs: New test.
	* rust/compile/decl_macro6.rs: New test.
	* rust/compile/decl_macro7.rs: New test.
	* rust/execute/torture/decl_macro1.rs: New test.
	* rust/execute/torture/decl_macro2.rs: New test.
	* rust/execute/torture/decl_macro3.rs: New test.
	* rust/execute/torture/decl_macro4.rs: New test.

Signed-off-by: Raiki Tamura <tamaron1203@gmail.com>