Update my person

Partial update of the caller's own person. A first_name or last_name in the patch is also copied onto the account display name teammates see in the directory and in group member lists: onto every one of the person's accounts when the person's own login session makes the edit, and onto the calling account alone for an API key, OAuth app or exchanged token, which act in one workspace. A non empty first_name or last_name must be at most 100 characters, contain a letter, and hold no control or invisible characters (400 invalid_name); an empty one clears it.