Support ConEnmu progress OSC
The 9;4 sequences can be used to show and hide progress on the tab bar. The error, indeterminate, and paused states are not implemented yet.
If a tab has a custom color, its color is used for the progress, otherwise the standard highlight color is used.
[1] https://conemu.github.io/en/AnsiEscapeCodes.html#ConEmu_specific_OSC
This is used by systemd 257 during progress reporting: https://mastodon.social/@pid_eins/113406672373007116
Also needs a bit of docs in the code
With custom tab color:
