gccrs: expansion: Correctly expand $crate metavar

gccrs: expansion: Correctly expand $crate metavar

gcc/rust/ChangeLog:

	* expand/rust-macro-expand.cc: Use new SubstituteCtx API.
	* expand/rust-macro-expand.h: Likewise.
	* expand/rust-macro-substitute-ctx.cc: Implement proper expansion of $crate.
	* expand/rust-macro-substitute-ctx.h: Adapt APIs to take macro definition when
	substituting.
	* util/rust-hir-map.cc (Mappings::insert_macro_def): Store crate information when
	inserting macro definition in mappings.
	(Mappings::lookup_macro_def_crate): New.
	* util/rust-hir-map.h: Adapt mappings to store crate in which macros were defined.

gcc/testsuite/ChangeLog:

	* rust/execute/crate-metavar1.rs: New test.
	* rust/compile/crate-metavar1.rs: New test.