Can't select large spans of text in the GUI

[ricab]

The Multipass GUI does not support selecting text spanning more than one screen:

• Pulling a selection beyond the screen doesn't cause the terminal to scroll
• Scrolling while selecting causes the selection to move
• Click, ctrl+click doesn't cause text to be selected at all

Hi; to clarify I meant in your app; if you select a part of text and want to continue above or below the current screen (so part of the previous or next screen) you can't do that.

Originally posted by @alexio-dev in #4250