Add support for OSC 8 sequences (hyperlinks)

[danschwarz]

OSC 8 is a relatively new escape sequence supporting HTML-like anchors in terminal emulators. GNOME Terminal, iTerm2, Windows Terminal and other terminal apps all support this sequence in their recent versions. Details are here.

Here's a simple command to try out the feature. The result is equivalent to this HTML link: This is a link

printf '\e]8;;http://example.com\e\\This is a link\e]8;;\e\\n'

Using Mosh 1.4.0 client and server, ubuntu 22.04 on both, with Windows Terminal 1.15.3466.0 the OSC 8 links are not passed from the server to the client. Using a recent version of OpenSSH instead of Mosh, the OSC 8 links are passed correctly.