[Terminal] Add Markers, Move/Select/Delete to Previous/Next mark

[dwt]

Zed is missing some of the best features of the MacOS Terminal. Namely its MARK feature.

The MacOS Terminal Sets a mark whenever the it waits for user input (not perfect but close) and then allows me

• to move quickly between marks (⌘-↑/⌘-↓) - this is insanely useful if you have commands that produce a lot of output, like build logs
• Select between marks (⌘-⇧-↑/⌘-⇧-↓) - very useful if you want to quickly share the output of the last command in a chat or bug report
• Delete the output of the last command (⌘-L) - very useful if you tried something, it didn't work out, and you would like to see the output before that again to work off of that.

I use these all the time, and frankly find that I not use the internal terminal because of that.