Format libcore with rustfmt

This commit applies rustfmt with default settings to files in
src/libcore *that are not involved in any currently open PR* to minimize
merge conflicts. The list of files involved in open PRs was determined
by querying GitHub's GraphQL API with this script:
https://gist.github.com/dtolnay/aa9c34993dc051a4f344d1b10e4487e8

With the list of files from the script in `outstanding_files`, the
relevant commands were:

    $ find src/libcore -name '*.rs' | xargs rustfmt --edition=2018
    $ rg libcore outstanding_files | xargs git checkout --

Repeating this process several months apart should get us coverage of
most of the rest of libcore.

src/libcore/task/mod.rs

@@ -8,4 +8,4 @@ pub use self::poll::Poll;
 
 mod wake;
 #[stable(feature = "futures_api", since = "1.36.0")]
-pub use self::wake::{Context, Waker, RawWaker, RawWakerVTable};
+pub use self::wake::{Context, RawWaker, RawWakerVTable, Waker};