Clean up some lifetimes in `rustc_pattern_analysis`
This PR removes some redundant lifetimes. I figured out that we were shortening the lifetime of an arena-allocated `&'p DeconstructedPat<'p>` to `'a DeconstructedPat<'p>`, which forced us to carry both lifetimes when we could otherwise carry just one.
This PR also removes and elides some unnecessary lifetimes.
I also cherry-picked 0292eb9bb9b897f5c0926c6a8530877f67e7cc9b, and then simplified more lifetimes in `MatchVisitor`, which should make #119233 a very simple PR!
r? Nadrieril
e1be642b41