feat: Add strings 'You left the channel.' and 'Scan to join Channel'

[Hocuri]

Close #7233

Part of #6884

[iequidoo]

Couldn't "You left the chat" replace the two different strings?
And maybe my Spanish is bad, but "Te fuiste" sounds good to me, also "Вы вышли" in Russian.

[r10s]

strings and changes in ffi are missing, i do a PR

[r10s]

Couldn't "You left the chat" replace the two different strings?

yes, that would have been an alternative with less noise, it somehow did not came to mind before :) however, having now two strings is good as well, from view of user even better. no need to change again

[Hocuri]

Both has its pros and cons, but it's not that important, I agree with going with the thing that was already done now.