Switch out spotless for an alternative

[lukebemish]

Spotless has... some quirks. Among others:

• the author dislikes gradle's configuration cache conceptually, and spotless's support for it is generally iffy, including using some... questionable workarounds
• a good bit of formatting logic is dependent on the JVM used to invoke gradle, and cannot change with the toolchain -- this is... not optimal, when you'd like a neo-dev environment to be pretty easy to have Just Work on most machines with a somewhat recent JVM present locally.
• Sometimes its cache gets... wacky, and just doesn't recognize files as needing re-formatted
• Running gradle with a different java version than you are developing for causes... issues, due to how spotless invokes formatters.

immaculate is a spotless alternative built with a much narrower scope (namely, the sort of formatting you tend to see in java projects like this), designed to utilize built-in gradle features when possible (up-to-date checking and incremental tasks for figuring out which files to re-check), prefer lazy configuration, and respect gradle best practices whereever I have any clue what they are; this PR switches neo-dev to use it instead of spotless. Note that, due to using the same version of eclipse JDT and the same other formatting steps besides that, no formatting has shifted compared to using spotless.

immaculate is new and thus rather untested; spotless is a much more established plugin, but also has a much more established set of issues, some of which seem to be continually popping up in discord (the notable one here is the whole bit where tons of stuff is dependent on the java version used to invoke gradle). Furthermore, this change could probably use some more extensive testing to make sure it behaves right in a number of different development environments.

In any case, this PR could use testing on different environments to make sure it's all behaving sensibly across dev environments.

[neoforged-pr-publishing]

• Publish PR to GitHub Packages

[sciwhiz12]

Untested yet, but looks clean enough. I have a few spots that need some explanation, though.

[neoforged-automation]

@lukebemish, this pull request has conflicts, please resolve them for this PR to move forward.

[neoforged-releases]

🚀 This PR has been released as NeoForge version 21.4.22-beta.