Known folders can be redirected using `SHSetKnownFolderPath`, and it's a bit iffy to rely on environment variables.
This also more easily allows us to add `user_*_dir` procedures for the remaining 139 GUIDs in `known_folders.odin`, provided they have equivalents on other platforms.
This patch simplifies the implementation and fixes#5254.
Previously, the mutex was set up as if there could be multiple writers,
and there seemed to be some confusion as to which `Writer` bits to
check, as not all were checked or set at the same time.
This could also result in the mutex being left in a non-zero state even
after unlocking all locks.
All unneeded state has been removed and extra checks have been put in
place.
When trying to grab the window pointer off the notification in a
windowDidBecomeKey implementation, I kept getting segfaults calling
notification->object(). The second argument of these needs to be a SEL.
https://developer.apple.com/documentation/objectivec/class_addmethod(_:_:_:_:)?language=objc#Discussion
I imagine existing code is getting by by setting the window information
in the delegate's context userdata, which works fine when you only have
one window as you can avoid needing to call notification->object(),
until you want one delegate assigned to two windows, hard to work around.
In `.Multiline` mode:
- `^` is now defined to assert the start of the string or that a "\n" or
"\r" rune was parsed on last VM dispatch.
- `$` is now defined to consume a newline sequence of "\n", "\r", or
"\r\n" or to assert the end of the string.
The check seems to have been assuming that rune comparisons are
unsigned, but they're signed. This was causing an assertion failure for
certain input characters (anything with an ASCII value less than
'+'/43).
