Update suffixed literal support

[ehuss]

Suffixed literals have been undergoing recent changes, and there are some oddities to consider.

"foo"suffix is accepted in some situations rust-lang/rust#60494

Tuple index (a.1i32) is temporarily allowed: rust-lang/rust#60210

Attribute literals cannot have suffixes for the = TOKEN_TREE form. #![foo=1u32] is not allowed. However, since these are only built-in attributes AFAIK, may not be worth covering.