Add mouse support for the sidebar and output pane - #25

Thanks for this PR! I have some concerns here:

• Scrolling output with the mouse should already work, as long as the pane is focused (I understand that's part of the intention of the PR, to scroll where the mouse is positionally, but just stating the size of the win here)
• In testing this, I seem to have lost the ability to select text normally. Seems like I can get it back by holding down the option key but that doesn't feel very intuitive.
• A good chunk of this work is re-inventing Ink's createInputParser, not clear as to why

• Scrolling output with the mouse should already work, as long as the pane is focused (I understand that's part of the intention of the PR, to scroll where the mouse is positionally, but just stating the size of the win here)

The reason I missed the existing mouse-scrolling functionality is that in iTerm2, “Automatically enable alternate mouse scroll” is disabled by default, which prevents the feature from working. After enabling it, the functionality worked very well.

If enabling the terminal setting is sufficient for the existing functionality to work, then the changes in my PR might be unnecessary.

Ah ok, that makes sense, didn't realize that was off by default. I think we're probably good here then, thank you again! We can re-visit of you feel something else mouse-related falls short.