Rollup merge of #88041 - Aaron1011:deny-proc-macro-hack, r=wesleywiser

Rollup merge of #88041 - Aaron1011:deny-proc-macro-hack, r=wesleywiser

Make all proc-macro back-compat lints deny-by-default

The affected crates have had plenty of time to update.
By keeping these as lints rather than making them hard errors,
we ensure that downstream crates will still be able to compile,
even if they transitive depend on broken versions of the affected
crates.

This should hopefully discourage anyone from writing any
new code which relies on the backwards-compatibility behavior.