Rollup merge of #77582 - ecstatic-morse:disable-early-otherwise-branch, r=wesleywiser

Move `EarlyOtherwiseBranch` to mir-opt-level 2

cc #75119

This didn't have an [effect in most cases](https://perf.rust-lang.org/compare.html?start=81e02708f1f4760244756548981277d5199baa9a&end=2e0edc0f28c5647141bedba02e7a222d3a5dc9c3&stat=instructions:u), and is not trivially sound. Let it bake at `mir-opt-level=2` for a while.

Also, this missed the cutoff for beta, so we'll have to backport this.
r? @wesleywiser