Don't attempt to complete against package names if the user is trying to
enter a switch to speed things up.
Also work around #5267 by not wrapping unfiltered `all-the-package-name`
calls in a function.
bower was calling `__fish_should_complete_args`, the old name for
`__fish_should_complete_switches.`
yarn was parsing bower.json instead of package.json.
Now parses package.json and uses results to provide a list of possible
completions to `yarn remove`. There may be other subcommands that could
benefit from this.
Could have parsed yarn output, but yarn is slow and packages.json format
is generally standard since it's machine-generated json.
