Implement better semantics for unverifiable code.

Implement better semantics for unverifiable code.

	* verify.c (mono_method_verify_with_current_settings): Add
	extra param telling if the method should be treated as fulltrust
	regardless of verifier settings.

	The only implication of this is that fulltrust verification
	can't stop on the first unverifiable error like verifiable
	code can. This only impact unverifiable methods running
	on non standard verification setups.

	* mini.c (mini_method_verify): If the verifier is enabled
	and the method belongs to an assembly with a valid skip
	verification token (the UnverifiableCodeAttribute cattr)
	the code will be checked now for errors instead of simply
	been ignored.

	This patch gives --verify-all much more saner behavior
	for assemblies with unsafe code.

	Fixes #676054