Rollup merge of #138442 - dianne:deref-pat-euv-fix, r=compiler-errors

EUV: fix place of deref pattern's interior's scrutinee

The place previously used here was that of the temporary holding the reference returned by `Deref::deref` or `DerefMut::deref_mut`. However, since the inner pattern of `deref!(inner)` expects the deref-target type itself, this would ICE when that type was inspected (e.g. by the EUV case for slice patterns). This adds a deref projection to fix that.

Since current in-tree consumers of EUV (upvar inference and clippy) don't care about Rvalues, the place could be simplified to `self.cat_rvalue(pat.hir_id, self.pat_ty_adjusted(subpat)?)` to save some cycles. I personally find EUV to be a bit fragile, so I've opted for pedantic correctness. Maybe a `HACK` comment would suffice though?

Fixes #125059

r? `@compiler-errors`

Author: jhpratt