Loading a wearable hangs or is slow for some users

When loading a new asset the "new item" window sometime hangs. This is probably related to the usage of the 3D libraries or the WearablePreview to generate the wearable's thumbnail.

A way to fix this could be to move the procedure to generate the wearable's thumbnail into the next step of the modal and show a loading indicator while the thumbnail is being generated.

Example of a wearable hanging: [https://discord.com/channels/417796904760639509/846510210352807976/1048218849935372379](https://discord.com/channels/417796904760639509/846510210352807976/1048218849935372379)