Use NonZeroU32 as the backing type for Keysym

[notgull]

X11 generally uses the NO_KEYSYM value, as alias for zero, to denote that a keysym is not present. Therefore it would make sense to use a NonZeroU32 as the backing type for the Keysym type instead of u32. This way, for Option<Keysym> there is no ambiguity between None and Some(NO_KEYSYM).

Cons:

• There may be a necessary difference between None and Some(NO_KEYSYM).
• Requires raising the MSRV to 1.57 (although most of the windowing ecosystem is past that already so I wouldn't mind).

[kchibisov]

The main issue is that passing around in FFI is a bit awkward for such a type.

[notgull]

I suppose. Although it would be safe to use as the input for a function, and Option<Keysym> is fully FFI safe.

[kchibisov]

Ah, yes, that's true. Well, we could do so, I guess, but the thing is that not all crates do Option<Keysym> and I think you'd need to convert.