Expanded polygon editor closes when selecting another tile

[KoBeWi]

Tested versions

4.4 db66bd3

System information

Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 (NVIDIA; 31.0.15.4633) - Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz (8 Threads)

Issue description

Introduced in #95034

bB76LVVu3O.mp4

Technically it's not a regression, because it fixed a worse issue, but it can still be improved.

More info from the PR:

TileSet editor has an internal inspector that really likes getting refreshed. One instance is when you select another tile, another is when a polygon is added or removed:

godot/scene/resources/2d/tile_set.cpp

Line 6271 in 3978628

notify_property_list_changed();

This causes all property editors to get destroyed and re-created.
There is one special editor though - the expanded editor. When you expand polygon editor (see #79512), it's moved to a different parent that isn't inside the inspector. So when inspector is cleared, the expanded editor survives it and holds outdated information.

I don't have a good solution for that yet. Perfectly, when inspector is refreshed, the previous editor should be automatically expanded again. However the "previous" editor no longer exists and there can be multiple polygon editors, so it has to be somehow remembered per-property, idk.

Steps to reproduce

1. Edit TileSet
2. Edit some tile's polygon
3. Expand the editor
4. Select another tile

Minimal reproduction project (MRP)

N/A