AppKit Improvements (Getting TextEdit to compile and Run)

[CKegel]

Adds stubs and implements missing functionality as required for Apple TextEdit to compile and run. Also note the following related PRs: :white_check_mark: CoreFoundation :white_check_mark: LaunchServices :white_check_mark: AppleEvents Stubs :white_check_mark: TextEdit CMake

Fixes Issue 383

[CKegel]

I'm working on finalizing this PR, and I plan to do the following before I'd consider it ready to merge(after review):

1. Solidify the implementation of [NSAttributedString initWithData:]
2. Ensure File Type and UTI to Document Class parsing/identification are working correctly
3. review the code for style and memory leaks and refactor

After this PR is eventually merged, I'd like to create an issue where I can track progress on the rest of my AppKit improvements for TextEdit as, while this PR makes great strides, it doesn't even come close to making TextEdit run perfectly. Let me know what ya'll think and I'll be back to implement it after my final exams have wrapped up next week!

[CKegel]

Now we are getting close! I've started using the formatting tool before every commit, so hopefully there should be less style/formatting issues. I've also managed to squash the commits in a way that I believe makes sense. I believe I've properly made all of the requested changes, but if not I'm happy to continue making adjustments!

[CuriousTommy]

@bugaevc I don't remember if we talk about this before, but I'm thinking of merging this as is, unless you have any objections.

[bugaevc]

Please do. Whatever remaining objections/corrections I might/would have had would be better dealt with after the fact, compared to keeping this stalled indefinitely.

[CuriousTommy]

Thank you for your contribution @CKegel!