rust: Lower minimum supported Rust version to 1.49

rust: Lower minimum supported Rust version to 1.49

gcc/rust/ChangeLog:

	* checks/errors/borrowck/ffi-polonius/Cargo.lock: Regenerate.
	* checks/errors/borrowck/ffi-polonius/Cargo.toml: Update to use source patching instead of
	vendoring, lower edition to 2018.
	* checks/errors/borrowck/ffi-polonius/vendor/log/Cargo.toml: Change edition to 2018.
	* checks/errors/borrowck/ffi-polonius/vendor/log/src/lib.rs: Remove uses of unstable
	feature.
	* checks/errors/borrowck/ffi-polonius/.cargo/config.toml: Removed.

libgrust/ChangeLog:

	* libformat_parser/Makefile.am: Avoid using --config as it is unsupported by cargo 1.49.
	* libformat_parser/Makefile.in: Regenerate.
	* libformat_parser/generic_format_parser/src/lib.rs: Use extension trait for missing
	features.
	* libformat_parser/src/lib.rs: Likewise.
	* libformat_parser/.cargo/config: Moved to...
	* libformat_parser/.cargo/config.toml: ...here.