Following changes are implemented:
- Add 'clap::Arg::get_visible_aliases(&self)' method
This new method provides access to visible argument aliases
- Add 'clap::Arg::get_short/long_and_visible_aliases
This new method provides access to the short/long arguments and its
visible aliases
- Add visible aliases completions in clap_generate for following shells:
- Bash
- Elvish
- Fish
- Powershell
- Zsh
- Add test fixtures for testing visible alias completions in clap_generate:
'clap_generate/tests/completions/<shell>::<shell>_with_aliases()'
compgen takes exactly one "word" argument; if multiple are passed, it
will ignore all but the first. If `$cur` is not quoted and contains
whitespace, it will be expanded into multiple words, so the completions
will be based only on the first word of `$cur`, which is clearly not
correct.
To fix this, quote `$cur` to prevent word splitting, where necessary
(Bash does not perform word splitting inside the extended test command
`[[`, so quotes aren't necessary there).
