Fix tap constants.

[reitermarkus]

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Accept any tap name, as long as it is a valid directory name, i.e. doesn't contain slashes in user or repo.

Fixes #16727.

[MikeMcQuaid]

Thanks for the quick fix but: why do we need to permanently widen the range of acceptable tap names to fix this regression?

[reitermarkus]

@MikeMcQuaid, for example, brew tap <user>/<repo> doesn't validate the name at all, except for the check for slashes in Tap.fetch. So this was always broken in these regexes (and in Tap::from_path which uses them), we just weren't using them consistently for every loader in Formulary before, and we weren't using Tap::from_path in Tap::each before.

[MikeMcQuaid]

@reitermarkus Ok. I'd like in future changes like this that are not strictly a fix but an actual functionality change to have some discussion before a critical self-merge, thanks.

[reitermarkus]

It doesn't change functionality though, except for making Tap::from_path consistent with what we actually allow in other places (e.g. Tap::fetch). Note that e.g. brew install some/tap.with.dots/myformula always worked, we just didn't use these regexes consistently in Formulary before.