CheckLoopVisitor: also visit closure arguments
This turns the ICE #50581 in this code:
```rust
fn main() {
|_: [u8; break]| ();
}
```
from
```
'assertion failed: self.tcx.sess.err_count() > 0', librustc_typeck/check/mod.rs
```
to
```
librustc_mir/hair/cx/expr.rs:543: invalid loop id for break: not inside loop scope
```
which is an ICE as well but at a later stage during compilation and most importantly
fixes of bug #50576 will fix this as well.
As this "only" moves an ICE to a later stage, I didn't add any tests.
Now I have manually verified the default impls of the visitor trait to check whether we have missed any other opportunity to visit more stuff and coudln't find anything (except the missing `break` visit I've fixed in #50829 but that one was already r+'d so I didn't want to push more commits).
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