Implement text checking panel using NSTextCheckingController.

[gcasa]

Implement text checking panel using NSTextCheckingController.

[DTW-Thalion]

The class was a complete skeleton: every one of its methods had an empty body and the spell document tag stayed at zero, so a client wired to one got nothing back.

#869 implements it. The controller takes a unique spell document tag, asks its client for the text of a range and honours the shorter range a client may return, marks what the checker finds with the spelling state attribute, carries on from the end of the selection so that asking again steps to the next word, applies a correction and reselects it at the length of the replacement, ignores a word for its own tag, offers the guesses for a marked range as a menu, and stops touching the client once invalidated. Those behaviours were measured against AppKit before being written.

That does not finish what the title asks for. showGuessPanel: orders the existing spelling panel front, but there is no substitutions panel here to order front, so orderFrontSubstitutionsPanel: is left empty, and the candidate list methods have nothing to work with. A text checking panel of its own is a design question rather than a missing call, so I have not invented one.

Worth knowing for anyone testing this area: GSspell.service advertises NSLanguages = (AmericanEnglish), while NSSpellChecker starts on language English. On a machine where that is the only service installed, nothing is ever contacted, the log reads "Service to start: (null)", and every check comes back with an empty range. setLanguage: does not get around it, because the list of languages comes from the server that has not started. That is why seven of the assertions in the new test are guarded rather than unconditional.