Experiment with display the Find/Replace Overlay as a Part in a Partstack instead of an overlay shell.

Caveats:

• the part has the annoying tendency to stick to the side instead of allowing to be "positionned to the top all the time"
• keypresses are still interpreted as keypresses targeted towards the Editor behind (ie. pressing Ctrl+Backspace delets a full word in the editor not in the overlay)

First time opening the overlay (something is wrong...)

Second time pressing Cltr+F

Adapted from #2093

I do not believe that this solution can bring improvement to #2099