Provide a way to include rarely used characters in Person names

[jennifer-richards]

Description

In response to creation of spam-purveying Person records, #7453 disallowed : and / in all name-like fields of the Person record. This added to the existing ban on @ characters.

The intention behind this is to avoid abuse, and every current case where : or / was present in a name was either a very clearly abusive name (showing a URL on a profile, ascii art, attempts to find SQL backdoors, etc) or perhaps, charitably, someone who was confused about how to use the fields properly.

Outright banning these characters in names is bad from an inclusivity perspective. While rare, there may be (and probably are) legitimate situations where these punctuation marks are needed to correctly represent a person's name. We should provide a path to adding such a name in these situations.

Given that we don't know of any cases where this is needed, and that we do have at least several dozens of examples of abuse, we should adjust the validation so that any characters that do not cause technical problems can be entered via the admin but cannot be entered by users directly.

This will be a little bit tricky because we'll need to be sure that after such a name set, the user can still adjust the rest of their profile.

I'm marking this as "minor" because we don't know of a case where it'll be used, but it'd obviously become more urgent if we encounter one.

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