Update lifetimes for pre-expansion validation

[ehuss]

This updates the lifetime grammar to accommodate rust-lang/rust#126762 which switched to validating lifetimes pre-expansion. It also fixes a minor oversight where 'static was always grammatically allowed in a lifetime generic parameter (but is rejected semantically).

In summary, since this is subtle: Labels no longer parse '_ as valid. Thus, '_ is removed from the LIFETIME_OR_LABEL token. Since '_ is allowed by lifetimes, it has been moved to Lifetime.

Example:

// This is now an error in 1.81.
#[cfg(any())]
fn f() {
    '_: {
        break '_;
    }
}

and the oversight that was fixed (this was always allowed, but wasn't reflected in the reference grammar):

#[cfg(any())]
fn f<'static>() {}

cc @compiler-errors