Support loading game and mods from classpath for dev configurations

[Floweynt]

Motivation

When doing development, it's often beneficial to be able to easily run the server in a development environment (mojmapped everything). This enables features like class/mixin hotswapping.

This pull request implements loading mods and the target game from the classpath, which can be set to contain the mod classes and a mojmap server.

I have done some preliminary testing, and it doesn't seem to break other mod loading options.

Dev Env Setup

With this PR, developers can change the following to set up a sane environment:
Add the following dependencies to the runtime classpath:

implementation("space.vectrix.ignite:ignite-launcher:$igniteVersion") // this needs to be published to maven
implementation("io.papermc.paper:paper-server:userdev-$paperVersion")
implementation("com.lmax:disruptor:3.4.2") // I don't know why this is needed

For IntelliJ, add an application configuration with:

• Classpath: module project-name.main
• VM options (you may need to enable adding vm options with modify options dropdown): -Dignite.locator=classpath
• Main class: space.vectrix.ignite.IgniteBootstrap
• Program args: -nogui
• Working dir: $PROJECT/run/

Bonus: mixin hotswap works as expected, see the fabric guide