Wayland: Add support for wlr_screencopy_unstable_v1 on wlroots base compsitors

[Zai-Kun]

On my machine with archlinux and sway, when trying to take a screenshot it throws this error: thread 'main' panicked at src/main.rs:13:45:
called Result::unwrap() on an Err value: DbusError(D-Bus error: No such interface “org.freedesktop.portal.Screenshot” on object at path /org/freedesktop/portal/desktop (org.freedesktop.DBus.Error.UnknownMethod))
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

It would be nice if xcap also used the wlr_screencopy_unstable_v1 for wlroots based compositors like mine. Would this feature be possible?

this might be helpful: https://gitlab.com/redArch/wayland-screencopy-utilities/-/blob/main/gazo