Corruption of .import ConfigFile settings when an external BoneMap was renamed or deleted.

[lyuma]

Tested versions

• 4.3.stable
• All older versions of 4.x (crashes)

System information

Godot v4.3.stable - Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3090 (NVIDIA; 32.0.15.6094) - Intel(R) Core(TM) i9-9900K CPU @ 3.60GHz (16 Threads)

Issue description

#93284 was merged as an emergency fix for 4.3. It avoids a crash, but does not prevent corruption of import settings or avoid import failures due to the same underlying issues.

In particular, this quote from the description should highlight why it is important that a bug still be open:
i think all these issues also have another underlying issue to them, this just turns the crashes into error prints

The following bugs were incorrectly closed as part of the fix:

• Crash when trying to edit a 3D model with an external bone map assigned that was renamed #90014
• The editor quits after deleting BoneMap #92940
• Renaming a bonemap and opening a .blend resource which was configured with this bonemap and also reimported will cause a crash, #84371

Therefore I'm opening this issue so that we can track the underlying problem and attempt to address it in a better way for 4.4.

Note that the underlying issue relates to var_to_str() and ConfigFile APIs and their mishandling of missing resources as well as lack of UID serialization, so I'm going to include this as a core issue since it is critical.

This issue caused by deleting referenced files from .import blocks making improvements to the advanced importer and material editing:

• Improve 3D Asset Import Dialog material editing #86430

Steps to reproduce

1. Import a 3D model with a Skeleton.
2. Create a bone map for it and right click it to save it externally.
3. Rename the external resource of the new bone map.
4. Attempt to open the advanced import dialog for the model.

Minimal reproduction project (MRP)

https://github.com/godotengine/godot/files/14803641/bone_map_crash.zip