contracts: fix lowering final declaration without trailing semicolon
Lowering for contract delcarations introduced in rust-lang/rust#144444 incorrectly handled the final declaration statement when it didn't end in a semicolon. This change fixes the issue.
See the included regression test for the minimal reproducible example.
Contracts tracking issue: https://github.com/rust-lang/rust/issues/128044
Stuart Cook
3c2a5dbace