Minecraft 1.21 Support

[hammy275]

This was already planned for 1.5.0 Beta 2 for a while now, but I'm opening it as an issue so it's more easily tracked.

Given the current progression of development, this is very likely going to specifically be 1.21.1 for this ImmersiveMC verison. 1.20.6 will be skipped.

[hammy275]

1.21.1 is significantly different, so even though I have something that compiles and runs well, there's several regressions that will need fixing before this is ready to go. This is a list of the ones that I've found so far, but likely is not complete:

• [x] Bag doesn't render in config screen.
• [x] Beacon confirmation doesn't work.
  • It fails to match the effect with == in isValidForBeacon().
• [x] Lootr compatibility crashes when looking at a normal barrel or shulker box. Glad to see #369 doing its job, though!
• [x] Empty lecterns crash the game.
• [x] Text at the enchanting table isn't shown.
• [x] Lecterns only show the first two pages of a book, and always act as if you can't turn past the second set of pages. Held books are NOT similarly affected.
• [x] "Unable to fill loot container" Lootr errors Not fixing this (yet at least) since this only happens for Lootr containers that don't have loot tables. Outside of /give and similar, this shouldn't happen.

[hammy275]

Most major regressions are handled! Any others should be caught during testing before release.