moving to gradle / maven

[phu54321]

fixes #648

Good things:

• We can use maven and manage .jar dependencies using gradle. When one wants to upgrade the dependencies, one can just change build.gradle and it's done.
• gradle is much well-supported on popular IDEs. (android studio, IDEA) It's also the recommended build system by libgdx.
• Moving to lwjgl or porting code to other platforms (android / ios / html5) will be much easier. There are some conflicting packages (notably java-discord-rpc and jportaudio), but these dependencies could easily bypassed? (ex: macOS and ios doesn't require jportaudio for low-latency audio)
• Managing macOS arm64e build will be much manageable.

Currrent caveats:

• shadowJar (thing that consolidates library .jars to beatoraja.jar) embeds ALL unused libraries from javacpp-presets. (ex: opencv)

Maybe I could fix this, but first a working beatoraja source should first be public.

• current github source is 0.8.3, not 0.8.4
• current code won't run by itself. (See getTargetProperty("MAX") infinite recursion #712) I understand that IR related code should be kept private, but at least the public code should work without IR.

When these issues are resolved, I could fix those issues.