Copy text using OSC52

[naseschwarz]

This Pull Request closes #2366.

It changes the following:

• If copying using wl-clip or xclip and xsel fails, copy using OSC52 (Search for "Ps = 5 2").

This does not change the default behavior. On both wayland and X, wl-copy and xclip/xsel will be preferred. Only if one path fails, an OSC52 escape sequence will be issued.

I have tested this by running tmux, which has the option to turn support for this off and on (using :set -g set-clipboard off or :set -g set-clipboard on) and SSH. When tmux's clipboard support was off, no text was copied. Once I enabled it, copying worked as expected. From this I conclude that the whole setup works as expected.

N.B.: There is no easy path for gitui itself to check whether copying worked. Also, this essentially disables error reporting on wl-clip, xclip and xsel, as it acts as a fallback for these options.

I followed the checklist:

• I added unittests
• I ran make check without errors
• I tested the overall application
• I added an appropriate item to the changelog

[naseschwarz]

I'm also trying to get this into crossterm. If that were merged, we could consider using that instead.

[cruessler]

I’m going to add myself as a reviewer!

[cruessler]

I tested this PR on my Linux machine, using Alacritty, after having commented out the wl-copy block, forcing the usage of escape codes.

From my side, everything looks good!

[extrawurst]

Awesome once the CI is green (minus the lints) I will merge. Thank you both!

[naseschwarz]

CI failed as my split up copy function was only called on Linux and thus were marked as dead code on Mac OS and Windows. Should be fixed now.

make check fails due to #2554 now, though.

[naseschwarz]

I'm really sorry for bothering you because of build failures in CI, @extrawurst. My bad. I have now set up a CI run in my own namespace and, apart from cargo deny because of paste, it succeeds.

[extrawurst]

@naseschwarz Thank you!