Instanceof pattern: exclusion for Stream.collect(..)

[BoykoAlex]

Support instanceof with types where type parameters shouldn't be present in the instanceof.

For example:

if (o instanceof List) {
  map.put("key", String.join(",", (List) o));
}

currently produces a compiler error when refactored in:

if (o instanceof List<?> list) {
  map.put("key", String.join(",", list));
}

The compiler error:

The method join(CharSequence, CharSequence...) in the type String is not applicable for the arguments (String, List<capture#1-of ?>)

Instead it should become:

if (o instanceof List list) {
  map.put("key", String.join(",", list));
}

(i.e. without the wildcard)

The fix is if the type has type parameters and the following type casts statements cast to type with type parameters then wildcard type parameter(s) will be added. Otherwise no type parameters will be added to the type in the instanceof

[timtebeek]

Thanks for the work done here @BoykoAlex ! Let me know when you're done by marking the PR as ready for review. :)

[BoykoAlex]

Abandoned in favour of #338