feat(clap_complete): Support flags with values --flag barand -f bar in native completions

[shannmu]

related issue: #3920
what is left

• support -fbar and -f=bar
• error parsing for --flag=bar in bash
• foo --bar\t offering both --bar <value> and --bare

[shannmu]

The cases of -fbar and -f=bar have not been handled yet.

[shannmu]

I have added support for -fbar and -f=bar completion.

clap/clap_complete/src/dynamic/completer.rs

Lines 141 to 146 in 469d847

	completions.extend(
	shorts_and_visible_aliases(cmd)
	.into_iter()
	// HACK: Need better `OsStr` manipulation
	.map(|(f, help)| (format!("{}{}", dash_or_arg, f).into(), help)),
	);

This code didn't consider the case -f=bar[TAB], so it could generate -f=barf in completions. I will fix it later.

[epage]

While talked about this in the call, to not lose track of this

I have added support for -fbar and -f=bar completion.

Please split that out into another branch for a later PR so we can focus on getting the current PR merged.