This pulls in
- clap-rs/clap#5731 for `IFS` oddities I had
- clap-rs/clap#5733 with the hope that this makes `CARGO_COMPLETE_BASH cargo +nightly` just work

`clap` was completed next to `clap_complete` because `clap_complete`
depends on unstable features from `clap`.
None should have changed in this time window but I wanted to exercise
caution.

fix(complete): Fix problems on my machine

### What does this PR try to resolve?
This pulls in
- clap-rs/clap#5731 for `IFS` oddities I had
- clap-rs/clap#5733 with the hope that this makes `CARGO_COMPLETE_BASH cargo +nightly` just work

### How should we test and review this PR?

### Additional information

`clap` was completed next to `clap_complete` because `clap_complete` depends on unstable features from `clap`.
None should have changed in this time window but I wanted to exercise caution.

clap-rs/clap#5733 removed the rustup proxy so that
`CARGO_COMPLETE=bash cargo +nightly` works
(with a side benefit of removing the proxy overhead).

As a downside, cargo no longer knows it is running within rustup, so we
aren't reading `--target` candidates from rustup.

This changes the code to always try rustup.  It is likely a good enough
source, even if the user isn't currently using it.
The candidates should be about the same, just rustup hides some by
default.
Hiding just means it isn't shown by default but if only hidden
candidates match, then we show them.

clap-rs/clap#5733 removed the rustup proxy so that
`CARGO_COMPLETE=bash cargo +nightly` works
(with a side benefit of removing the proxy overhead).

As a downside, cargo no longer knows it is running within rustup, so we
aren't reading `--target` candidates from rustup.

This changes the code to always try rustup.  It is likely a good enough
source, even if the user isn't currently using it.
The candidates should be about the same, just rustup hides some by
default.
Hiding just means it isn't shown by default but if only hidden
candidates match, then we show them.