Creating a new directory causes a rescan which takes ages

[dodgyville]

Godot version:
3.1.x (master)

OS/device including version:
ubuntu, nvidia

Issue description:
Moving a file or creating a new directory causes godot editor to start "scanning files, please wait..." (stdout shows "call rescan!") and it sits at 97% for a minute or so.

Is this new? And is it possible to avoid this call or speed it up?

[rminderhoud]

I've also had the editor crash when moving a directory with a large amount of files/sub-directories and it starts the re-scan. Unfortunately I didn't capture the crash logs. I will see if I can reproduce.

[akien-mga]

Duplicate of #19991.