Stabilize noop_waker

[eholk]

Tracking Issue: #98286

This is a handy feature that's been used widely in tests and example async code and it'd be nice to make it available to users.

cc @rust-lang/wg-async

Creating as a draft PR because T-libs-api will need to consider this and do an FCP before merging.

[rustbot]

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[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

tests/pass/float_nan.rs ... ok
tests/pass/0weak_memory_consistency.rs ... ok

FAILED TEST: tests/pass/move-data-across-await-point.rs
command: MIRI_ENV_VAR_TEST="0" MIRI_TEMP="/tmp/miri-uitest-ewp271" RUST_BACKTRACE="1" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1/bin/miri" "--error-format=json" "--sysroot=/checkout/obj/build/x86_64-unknown-linux-gnu/miri-sysroot" "-Dwarnings" "-Dunused" "-Ainternal_features" "-Zui-testing" "--out-dir" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/miri_ui/tests/pass" "tests/pass/move-data-across-await-point.rs" "--edition" "2021"
error: test got exit status: 1, but expected 0
 = note: compilation failed, but was expected to succeed

error: actual output differed from expected
---

Location:
   /cargo/registry/src/index.crates.io-6f17d22bba15001f/ui_test-0.26.5/src/lib.rs:357

Backtrace omitted. Run with RUST_BACKTRACE=1 environment variable to display it.
Run with RUST_BACKTRACE=full to include source snippets.
error: test failed, to rerun pass `--test ui`
Caused by:
  process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/deps/ui-de50b20aa7a9761c --quiet` (exit status: 1)
  process didn't exit successfully: `/checkout/obj/build/x86_64-unknown-linux-gnu/stage1-tools/x86_64-unknown-linux-gnu/release/deps/ui-de50b20aa7a9761c --quiet` (exit status: 1)
Command has failed. Rerun with -v to see more details.
  local time: Sat Nov 16 02:15:12 UTC 2024
  network time: Sat, 16 Nov 2024 02:15:12 GMT
##[error]Process completed with exit code 1.
Post job cleanup.

[zachs18]

LocalWaker is itself still unstable, so I think this function should remain unstable, just under that feature gate?

Suggested change

	#[stable(feature = "noop_waker", since = "CURRENT_RUSTC_VERSION")]
	#[rustc_const_stable(feature = "noop_waker", since = "CURRENT_RUSTC_VERSION")]
	#[unstable(feature = "local_waker", issue = "118959")]