Investigate longer initialization time when opening an editor screen for the first time

[skyecodes]

Title says it all

[skyecodes]

The longer initialization time seems to be due to 2 things:

• The texture loading and caching,
• The MVC initialization.

To make the first screen loading time quicker, I've made 2 improvements:

• Preload the textures,
• Setup and render a blank item editor screen.

For Fabric, it's done during client resource pack reloading. For Forge, it's done at game initialization.

I'll keep this issue open but it already seems to have reduced the first screen opening delay by a lot.