Record the correct target type when coercing fn items/closures to pointers

[compiler-errors]

Self-explanatory. We were previously not recording the target type of a coercion as the output of an adjustment. This should remedy that.

We must also modify the function pointer casts in MIR typeck to use subtyping, since those broke since #118247.

r? lcnr

[lcnr]

can you also add a test which requires the sub for closures, is case nothing hit that before?

[lcnr]

@bors r+ rollup

[bors]

📌 Commit 5df13af has been approved by lcnr

It is now in the queue for this repository.

[compiler-errors]

What the heck -- this PR caused two regressions:

• Struggleton.TitleScreenBGM.23bd2077802ae42336a788678a462d067fc9aa20

[INFO] [stdout] error[E0308]: mismatched types
[INFO] [stdout]   --> src/lib.rs:30:4
[INFO] [stdout]    |
[INFO] [stdout] 30 | fn create_press_any_hook(ctx: &mut InlineCtx) {
[INFO] [stdout]    |    ^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
[INFO] [stdout]    |
[INFO] [stdout]    = note: expected fn pointer `unsafe extern "C" fn(&mut InlineCtx)`
[INFO] [stdout]               found fn pointer `unsafe extern "C" for<'a> fn(&'a mut InlineCtx)`

• kwap-0.10.0

[INFO] [stdout] error[E0282]: type annotations needed
[INFO] [stdout]   --> src/blocking/server.rs:98:8
[INFO] [stdout]    |
[INFO] [stdout] 45 | #[derive(Clone, Debug)]
[INFO] [stdout]    |          ----- in this derive macro expansion
[INFO] [stdout] ...
[INFO] [stdout] 98 |   Send(Addrd<platform::Message<P>>),
[INFO] [stdout]    |        ^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for reference `&net::Addrd<kwap_msg::Message<<P as Platform>::MessagePayload, _, <P as Platform>::MessageOptions>>`
[INFO] [stdout]    |
[INFO] [stdout]    = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)

I'll look into both of them, and revert this if not.