task: make JoinHandle::abort_handle public

[SparkyPotato]

Motivation

The AbortHandle API is currently only exposed through JoinSet. This makes custom, user-defined implementations of JoinSet-like wrappers impossible.

Solution

As mentioned in #4530, the abort_handle method is simply made public.

[Darksonn]

Gah! The change I suggested doesn't work on the multi-thread runtime, which is the default for #[tokio::main]. You'll need to change it.

thread 'main' panicked at '`time::pause()` requires the `current_thread` Tokio runtime. This is the default Runtime used by `#[tokio::test].', src/runtime/task/join.rs:7:2
stack backtrace:
   0: rust_begin_unwind
             at /rustc/2c8cc343237b8f7d5a3c3703e3a87f2eb2c54a74/library/std/src/panicking.rs:575:5
   1: core::panicking::panic_fmt
             at /rustc/2c8cc343237b8f7d5a3c3703e3a87f2eb2c54a74/library/core/src/panicking.rs:64:14
   2: core::panicking::panic_display
             at /rustc/2c8cc343237b8f7d5a3c3703e3a87f2eb2c54a74/library/core/src/panicking.rs:147:5
   3: tokio::time::clock::with_clock
             at ./src/time/clock.rs:49:29
   4: tokio::time::clock::pause
             at ./src/time/clock.rs:131:9
   5: rust_out::main::{{closure}}
   6: tokio::runtime::park::CachedParkThread::block_on::{{closure}}
   7: tokio::runtime::park::CachedParkThread::block_on
   8: tokio::runtime::context::BlockingRegionGuard::block_on
   9: tokio::runtime::scheduler::multi_thread::MultiThread::block_on
  10: tokio::runtime::runtime::Runtime::block_on
  11: rust_out::main
  12: core::ops::function::FnOnce::call_once
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[SparkyPotato]

I changed the examples to something similar to JoinHandle::is_finished

[Darksonn]

Thanks. LGTM.