`is_expr_identity_of_pat`: simplify using `(unordered_)over` (#15450)

This makes the last arm significantly shorter, but marginally shortens
the other ones as well

- I first removed the length comparisons from the match guards since
they were already present in `(unordered_)over`, but then brought them
back since they are quite a helpful "guard clause"
- It's a bit unfortunate that the `Slice`/`Array` arm can't use `over`
as well, which creates some asymmetry, but changing the signature of
`over` to accept arbitrary iterators felt like too much to me,
especially because we'd lose the ability to compare the lengths of the
two inputs (which could've been mitigated by `ExactLenIterator::len`,
but that method is still unstable AFAIR)

One other option would be to only use `unordered_over` in the last arm,
and not `over`, but I think `over` is not that bad..

changelog: none

0 files changed, 0 insertions, 0 deletions