Auto merge of #145003 - Kobzol:rollup-kgb216b, r=Kobzol

Rollup of 12 pull requests

Successful merges:

 - rust-lang/rust#144552 (Rehome 33 `tests/ui/issues/` tests to other subdirectories under `tests/ui/`)
 - rust-lang/rust#144676 (Add documentation for unstable_feature_bound)
 - rust-lang/rust#144836 (Change visibility of Args new function)
 - rust-lang/rust#144910 (Add regression tests for seemingly fixed issues)
 - rust-lang/rust#144913 ([rustdoc] Fix wrong `i` tooltip icon)
 - rust-lang/rust#144924 (compiletest: add hint for when a ui test produces no errors)
 - rust-lang/rust#144926 (Correct the use of `must_use` on btree::IterMut)
 - rust-lang/rust#144928 (Drop `rust-version` from `rustc_thread_pool`)
 - rust-lang/rust#144945 (Autolabel PRs that change explicit tail call tests as `F-explicit_tail_calls`)
 - rust-lang/rust#144954 (run-make: Allow blessing snapshot files that don't exist yet)
 - rust-lang/rust#144971 (num: Rename `isolate_most_least_significant_one` functions)
 - rust-lang/rust#144978 (Fix some doc links for intrinsics)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

src/stability.md

@@ -181,4 +181,7 @@ the `deprecated_in_future` lint is triggered which is default `allow`, but most
 of the standard library raises it to a warning with
 `#![warn(deprecated_in_future)]`.
 
+## unstable_feature_bound
+The `#[unstable_feature_bound(foo)]` attribute can be used together with `#[unstable]` attribute to mark an `impl` of stable type and stable trait as unstable. In std/core, an item annotated with `#[unstable_feature_bound(foo)]` can only be used by another item that is also annotated with `#[unstable_feature_bound(foo)]`. Outside of std/core, using an item with `#[unstable_feature_bound(foo)]` requires the feature to be enabled with `#![feature(foo)]` attribute on the crate. Currently, only `impl`s and free functions can be annotated with `#[unstable_feature_bound]`.
+
 [blog]: https://www.ralfj.de/blog/2018/07/19/const.html