Fix bash completion

[casperdcl]

• fix bash completion of files in cwd
  • filter non-DVC-files where appropriate
• fix potential name clashed
• replace $(compgen -f) with $(compgen -f -X \!*?.dvc)?
  • this would mean commands which expect any arbitrary file paths will NOT accept DVC-file paths
• fixes Autocomplete for file names doesn't work (partially) [bash] #1923

Caveats:

• still won't allow completion of subdir paths. That would require a major enough overhaul that it's probably for another PR.

[casperdcl]

btw just a quick check - is there any instance where a command should autocomplete with BOTH DVC-files as well as non-DVC-files?

[efiop]

btw just a quick check - is there any instance where a command should autocomplete with BOTH DVC-files as well as non-DVC-files?

@casperdcl pull/push/fetch/status/checkout 🙂 They all support specifying particular output instead of dvc-file.

[casperdcl]

Great this is mergeable then.