Slow FilePicker performance due to large amounts of assets/icons in single folder

[rikmarais]

Describe the bug
FilePicker.browse when changing a default icon, e.g. systems/zweihander/assets/icons/character.svg needs to browse 4172 icons in systems/zweihander/assets/icons, leading to significant and unnecessary delay.

There are 4172 icons in the systems/zweihander/assets/icons directory. On a local machine, this isn't very noticeable, but still leads to a delay of ~0.5 seconds to browse, before rendering the FilePicker.

However when your assets are hosted on a network drive instead of on the local disk, (e.g. the Forge's Assets Library), this browse on the populated directory can lead to a significant delay (on the scale of 5-10s). I imagine that this would happen when using any network drive, even S3 storage.

Proposed solution
Not all of the 4172 icons in systems/zweihander/assets/icons/ are in use by default.
Moving/duplicating the default icons that are in use for each actor type and each item type, at least, to a separate systems/zweihander/assets/icons/default folder will drastically increase FilePicker.browse's performance, on network drives and also local drives, leading to a smoother experience while still allowing navigation into the more populated folder if a different icon is needed.

Alternatively, organizing the icons in systems/zweihander/assets/icons/ by type/purpose/intent will also improve performance. Eg. conditions, creatures, effects, spells, items, etc.

To Reproduce
Steps to reproduce the behavior:

1. Blank world, new actor
2. Click actor portrait image to assign new image
3. Wait for FilePicker.browse to complete. Takes ~0.5s on local drive and significantly longer on a network drive.

Expected behavior
After a short browse, render FilePicker.

Screenshots

Additional context
While this might only strongly negatively affect user who are using network drives, it causes a non-zero delay on local drives as well, and would likely be more noticeable on slower drives like HDDs.