With the recent changes that let you resize the sidebar, we have a tab index for the splitter which allows resizing without using the mouse for greater accessibility. There are two other places which have resizing in Compass which could benefit from this ability -aggregation stages and the mongosh plugin.

This ticket involves moving the resizing handle to a shared place (compass-components), updating it to be more accessible (see attached screenshot using an `input` html element) and then using that in the 3 places we allow resizing.