Custom editor shortcuts get corrupted

[KoBeWi]

Godot version:
da05ca6

Issue description:
When you open the editor, the shortcuts you have assigned stop working. They appear as empty strings in the settings panel and upon inspecting the editor_settings-4.tres you can see that the shortcuts exist, but are empty (scancodes are removed; but interestingly the modifiers remain).

[Calinou]

I can reproduce this on commit 0c53f1f (specifically after rebinding the freelook keys to be AZERTY-friendly).

[akien-mga]

Possibly related to #18020, CC @bruvzg.

[bruvzg]

I can't reproduce it with current master, at least with newly assigned shortcuts. But shortcuts assigned before #18020 was merged will be invalid since scancode was renamed to keycode.

[KoBeWi]

Uh, I'm constantly switching between pre-Vulkan and master, so this is a problem for me .-.

[akien-mga]

Pre-Vulkan master branch is almost the same as the 3.2 branch, so I'd advise using that instead if you need a usable version. I don't think it makes much sense to add some compatibility glue for bindings made with 4.0.dev before #18020, as these older revisions will quickly be obsolete.

There's no (direct) concern in the 3.x to 4.0 migration since they use different editor settings files.

[KoBeWi]

So this can be closed I guess.
I'm using pre-Vulkan mostly for #35704.