- Reconfigured subclass creation, as there was a
subtle-but-big-when-it-hit bug in the prior method where bridge
callbacks would lose context of the appropriate delegate when calling
the trait method. The new approach found in `src/foundation/class.rs`
maps and caches subclass creation, and subclasses are now more
apparent when debugging from the Objective-C side as we can carry
their intended name/usage through. Not applied to all yet, but
eventually.
- Cleaned up a number of linter warnings that had grown over time.
- Delegate traits now require an associated const `NAME`, which is used
for subclass creation.
- (macOS) Toolbars now supported setting selected items, which is
typically used in preferences screens.
- (macOS) Windows now support setting the toolbar display style. On Big
Sur, this works as intended - it's a noop on older OS's that don't
support it.
- Support for system icons for macOS preferences windows.
Still a bit to go to flesh this all out, but it's getting there - at
which point then iOS supoort can be folded in easier.
