Feature/method signature intersection (#2647 )

* Refactor: Rework expected MethodSignatures.

- ParameterGroups are gone, with every signature now effectively containing a required leading group and an optional vararg trailing group. The prior flexibility made working them easy to get wrong, for example in the matching logic which would have been incorrect for leading vararg groups.
- Inject previously contained 2 optional groups (the target's params and the captured locals) but this was in fact incorrect, since the captured params are required if we want to capture any locals, so it is now (better) represented as 2 separate signature options.
- The distinction between `WARN_IF_ABSENT` and `ERROR_IF_ABSENT` is entirely removed. It was effectively unused since it only applied to captured Inject locals, which are varargs and therefore never "absent" (a separate inspection handles unused LocalCapture).
- ModifyArgs is in fact all-or-nothing wrt capturing the target parameters, and this is now reflected.

* Fix: Disallow non-int int-like types in @ModifyConstant.

Not sure why these are there, Mixin doesn't allow them.

* Fix: Disallow `nullValue` in `@ModifyConstant`.

It does not work and cannot ever work.

* stash

* stash

* finish general intersection

* cleanup

* stash

* stash

* fix general intersection

* stash

* fix tests

* return type only suggestions

* prioritise existing return type in modifier suggestions

* restore BeforeConstant's behaviour of ensuring only 1 discriminator is specified, and supporting wildcard matches

* Fix: Support `.class` constants in `@ModifyConstant`.

* Switch `@ModifyConstant` to a general signature type.

* int coercion kinda fixed ish

* fix int coercion properly

* cleanup

* proper int-like logic

* cleanup

* some docs and fixes

* fix return type solving

* Cache walked supertypes and improve handling of Object as a supertype.

* Cleanup

* Cleanup

* Small fixes

* Small fixes

* Fix: Suggest "ci" for coerced callba...