Rollup merge of #85564 - pnkfelix:issue-85435-readd-capture-disjoint-fields-gate...

Rollup merge of #85564 - pnkfelix:issue-85435-readd-capture-disjoint-fields-gate, r=nikomatsakis

 readd capture disjoint fields gate

This readds a feature gate guard that was added in PR #83521. (Basically, there were unintended consequences to the code exposed by removing the feature gate guard.)

The root bug still remains to be resolved, as discussed in issue #85561. This is just a band-aid suitable for a beta backport.

Cc issue #85435

Note that the latter issue is unfixed until we backport this (or another fix) to 1.53 beta