tap_auditor: use short names when checking exception lists

[Rylan12]

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For core formulae, Formula#full_name is the same as Formulae#name, but this is not true for other taps. The formula names that need to go in the exception lists are the short names (because this is what we compare them to during the audit and changing this adds backwards incompatibility). I think this makes sense because the lists are per-tap so short names are sufficient.

TapAuditor also checks to make sure that every formula listed in an exception list actually exists in that tap. This is done by comparing each entry to Tap#formula_names. There is a problem here because Tap#formula_names returns the full name of each formula in the tap. For core formulae, Formula#full_name is the same as Formulae#name, but this is not true for other taps. Therefore, adding an audit exception using the short name will fail the audit checking that it exists in the tap. For example, btb/open-watcom/open-watcom-v2 (from formula_names) is not the same as open-watcom-v2 (from the exception list).

See Homebrew/discussions#2005 (comment) or btb/homebrew-open-watcom#9

[BrewTestBot]

Review period skipped due to critical label.

[carlocab]

Do we want a tap.formula_short_names method, maybe?

[Rylan12]

Do we want a tap.formula_short_names method, maybe?

I'm not opposed to it but I'm not sure it's really necessary. This is the only place we'd use it so it just seems a bit silly.