addMixinsTo tasks make bad assumptions that result in task dependency loops

[lukebemish]

Currently, a addMixinsTo... task is created for every single jar task, and is made to depend on the compileJava task for the source set being configured: https://github.com/SpongePowered/MixinGradle/blob/master/src/main/groovy/org/spongepowered/asm/gradle/plugins/MixinExtension.groovy#L1024-L1043

Unfortunately, this has some problematic side effects. Namely, it means that making compileJava depend on any Jar task from the same project will immediately result in an unfixable task dependency loop. I discovered this while investigating an incompatibility between MixinGradle and Registration Utils, but it will pop up any time that you have, say, a compileOnly dependency on a local Jar task or the like.