Rollup merge of #121750 - Nadrieril:switchkind-if, r=matthewjasper

match lowering: Separate the `bool` case from other integers in `TestKind`

`TestKind::SwitchInt` had a special case for `bool` essentially everywhere it's used, so I made `TestKind::If` to handle the bool case on its own.

r? `@matthewjasper`

Author: matthiaskrgr