JSONGenerator for addons and docs.json improvements

[Efnilite]

Problem

• The docs.json can only be generated for Skript.
• The return types of expressions are not mentioned in docs.json.
• Events gathered from the @Events annotation do not follow the docs.json spec.
• StructEvent does not have docs.

Solution

The `docs.json` can only be generated for Skript.

JSONGenerator has been modified to allow creating an instance of JSONGenerator based on a SkriptAddon instance. To this extent, the `skriptVersion` property has been replaced with the `source` property.

"source": {
  "name": "Skript",
  "version": "2.12.1"
},

JSONGenerator also now uses the new Registration API to get all syntax registered by a specific addon.

Because this makes JSONGenerator not follow the DocumentationGenerator pattern, and since HTMLGenerator will soon be obselete, DocumentationGenerator has been deprecated, alongside JSONGenerator#generate().

The return types of expressions are not mentioned in `docs.json`.

A new `returns` property has been added to expressions which determine what types an expression can return. This is currently only limited expressions that have a constant return type (i.e. not dependent on the input of the expression).

Events gathered from the `@Events` annotation do not follow the `docs.json` spec.

Given that the source events cannot be gathered from the contents of the `@Events` annotation, currently, the id of the event and the name of the event are the same. Given `@Events({"x", "y"})`, the resulting json code would be:

"events": [
  { 
    "id": "x",
    "name": "x"
  },
  {
    "id": "y",
    "name": "y"
  }
]

This will be properly integrated when #7668 gets merged.

StructEvent does not have docs.

Added docs.

Testing Completed

Manual testing.

Supporting Information

Breaking changes

• Updated the JSONGenerator version to 2.0.
• Removed the skriptVersion property and replaced it with the source property, which details the addon that this file was generated from.
• Events gathered from the @Events annotation are now stored with an id and name, instead of as a plain string.
• Renamed the returnType property for functions to an array called returns, similar to the new returns property on expressions.
• Renamed the classes array to types.

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Completes: #7680
Related: none

[APickledWalrus]

Good work here

[APickledWalrus]

Looking really good, just a few things