Number keyboard support

[jbbjarnason]

Propagate hint of keyboard, tested only v1 code path.

To test I used a simple flutter code which sends number hint for a number text field, and wayland reference keyboard.

[martinetd]

To test I used a simple flutter code which sends number hint for a number text field, and wayland reference keyboard.

thanks, I'll try to give it a try next week-ish!

[martinetd]

I gave this a try earlier, it works fine on text input v3 as well (tested with squeekboard on niri, it doesn't work on weston and I couldn't get the weston-keyboard to display properly...)

I didn't figure out how to set view_properties_.use_onscreen_keyboard from my app so I kludged ELinuxWindowWayland::WlRegistryHandler to ignore it locally for testing, but once that was set the keyboard properly switches from number to text (also tested url)

A couple of remarks:

• the first commit adding cstdint has been fixed in fix: add missing cstdint header #2 so that commit needs to be dropped
• clang-format fails (test didn't run here but ran on the other repo)
• would be great if the commits could be squashed (rebased instead of merge, slightly more verbose commit message)

Since it's all small stuff I wanted to do it myself and push to your branch, but I don't seem to be able to (perhaps because the flutter-elinux org repo is not the original fork?...), so here's the commit:
martinetd@09dfdfd

Tests pass and I could merge this manually, but giving this a moment for others to look if you want.

I'll merge before tagging to 3.38.9 release if nobody looked until then

[martinetd]

Merged manually in 1e485df