Add Mixins to `New >` context menu

[supersaiyansubtlety]

Minecraft Development for IntelliJ plugin version

2024.1-1.7.5-477

Description of the feature request

It would be convenient if, when right clicking on a mixin package, the New > menu had options to create new mixin classes:

• an Accessor/Invoker Class item similar to Generate Accessor/Invoker
• a Mixin Class item
  • prompts for target class(es) to put in a @Mixin annotation
  • prompts (with checkbox) to extend+implement what the target class does (or in the case of multiple classes, whichever ancestors they have in common)
  • generates a dummy constructor if necessary
  • generates a package-private abstract class (I think those are the best defaults)
  • adds the new class to the mixins.json