Port to ESM
This MR ports the Shell UI to ESM modules based on the GJS work at gjs/!450 and gjs/!525
For the most part this is a 1:1 port between the old and new imports systems, some code must be refactored to work asynchronously:
- Panel indicator loading (to support dynamically checking if NetworkManager and GnomeBluetooth are available)
Extension loading (all JavaScript sources load asynchronously now) - !2364 (merged)