Auto merge of #65881 - anp:implicit-caller-location, r=eddyb,oli-obk

Implement #[track_caller] attribute. (RFC 2091 4/N)

Implements the `#[track_caller]` attribute in both const and codegen contexts.

The const implementation walks up the stack to find the nearest untracked callsite.

The codegen implementation adds an implicit argument to tracked function calls, and populates it with either a call to the previously-landed intrinsic or if the caller has `#[track_caller]` with a copy of the location passed to the current function.

Also includes a little cleanup and a few comments in the other caller location areas.

[Depends on: 65664](https://github.com/rust-lang/rust/pull/65664)
[RFC 2091 text](https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md)
[Tracking issue](https://github.com/rust-lang/rust/issues/47809)
[Tracking doc](https://paper.dropbox.com/doc/track_rfc_2091_impl-notes--Anf1NwnIb0xcRv31YLIadyj0Ag-rwCdRc2fi2yvRZ7syGZ9q#:uid=863513134494965680023183&h2=TODO-actually-pass-location-to)

src/librustc_feature/active.rs

@@ -541,5 +541,4 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::or_patterns,
     sym::let_chains,
     sym::raw_dylib,
-    sym::track_caller,
 ];