Implement Fn traits for Rc and Arc

[nvzqz]

These use the same semantics as the implementations for &F by only covering F: Fn.

This change enables passing reference-counted closures to functions that expect Fn + 'static or Fn + Clone.

ACP: rust-lang/libs-team#143

[rustbot]

r? @joshtriplett

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[rustbot]

Hey! It looks like you've submitted a new PR for the library teams!

If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

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

    Checking fluent-syntax v0.11.0
   Compiling zerofrom v0.1.1
    Checking tracing-subscriber v0.3.3
    Checking thorin-dwp v0.3.0
error[E0119]: conflicting implementations of trait `fmt::writer::MakeWriter<'_>` for type `std::sync::Arc<_>`
   --> /cargo/registry/src/github.com-1ecc6299db9ec823/tracing-subscriber-0.3.3/src/fmt/writer.rs:686:1
    |
674 | impl<'a, F, W> MakeWriter<'a> for F
...
...
686 | impl<'a, W> MakeWriter<'a> for Arc<W>
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `std::sync::Arc<_>`
For more information about this error, try `rustc --explain E0119`.
error: could not compile `tracing-subscriber` due to previous error
warning: build failed, waiting for other jobs to finish...
Build completed unsuccessfully in 0:03:06

[marmeladema]

See #71570 and #89771 for previous rejected attempts

[nvzqz]

Thanks for the links. I guess we can add this to the Rust 2.0 bucket list.