Migrate from `wlr-data-control-unstable-v1` to `ext-data-control-v1`

[w568w]

wlr-data-control-unstable-v1 has been standardized as ext-data-control-v1. The functionality is largely the same, but the interfaces are renamed.

Compositors:

• KDE 6.5 has completely dropped support for this wlr protocol, making this library unusable on KDE 6.5.
• Besides, Sway is also planning to drop it.

Libraries:

• wl-clipboard-rs has supported it but hasn't released yet.

That said, to maintain recent backward compatibility, it may be necessary to support both protocols.