Under FAF we now wrongly accept `final $($expr)?` in stmt position parsing it as `$($expr)?`

[fmease]

Note

Found thanks to @matthiaskrgr continuously fuzzing fmease/rasur versus rustc.
Downstream report: fmease/rasur#26.

With the introduction of FAF in PR #151783, we now wrongfully accept the following program (if the feature is enabled):

#![feature(final_associated_functions)]

fn main() {
    final;
    final 1 + 1;
    final { println!("text"); };
}

It essentially gets parsed as:

#![feature(final_associated_functions)]

fn main() {
    ;
    1 + 1;
    { println!("text"); };
}

[fmease]

cc @mu001999

[mu001999]

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