ignore higher-ranked object bound conditions created by WF
In the `issue-53548` test added in this PR, the `Box<dyn Trait>` type is expanded to `Box<dyn Trait + 'static>`, but the generator "witness" that results is `for<'r> { Box<dyn Trait + 'r> }`. The WF code was encountering an ICE (when debug-assertions were enabled) and an unexpected compilation error (without debug-asserions) when trying to process this `'r` region bound. In particular, to be WF, the region bound must meet the requirements of the trait, and hence we got `for<'r> { 'r: 'static }`. This would ICE because the `Binder` constructor we were using was assering that no higher-ranked regions were involved (because the WF code is supposed to skip those). The error (if debug-asserions were disabled) came because we obviously cannot prove that `'r: 'static` for any region `'r`. Pursuant with
our "lazy WF" strategy for higher-ranked regions, the fix is not to require that `for<'r> { 'r: 'static }` holds (this is also analogous to what we would do for higher-ranked regions appearing within the trait in other positions).
Fixes#53548
r? @pnkfelix
c22566d96d