Allow anchoring of terminal to a specific editor group

[sgronblo]

It seems the terminal can currently only be docker to the bottom of the editor or the right side of the editor. On a high resolution screen a lot of real estate is wasted on the terminal if most of the rows in the terminal are narrower than half the screen size. It would be better if I could have 2 or more editor groups open and anchor the terminal to the bottom of one of the editor groups instead of the bottom of the whole editor itself.

[Tyriar]

/duplicate #50853