Add keyboard shortcut to allow interacting with the UI while in the expression editor

Often while writing an expression, I'll need to refer to a property that isn't currently visible. In this case, I have to leave the expression editor to twirl down properties, and then have to open the expression editor again and find where I left off (and potentially have to resize the editor again).

It would be helpful, while the expression editor is active, to be able to hold down a key (eg. Alt), allowing the user to interact with other parts of the UI without closing the editor.