Java 16: Support and correctly handle relaxed static member rules and local interfaces, enums and records

[Marcono1234]

(These are new Java 16 feature so I can understand if you defer support for this to a later point.)
Blocked by #4281

Java 16 has the following two language changes which probably require adjustments in the extractor and in the CodeQL libraries and queries:

• As part of JEP 395 local enum and record classes and interfaces were allowed. The most important change here are probably local interfaces (since enums and records are likely covered by CodeQL's LocalCass).
  This requires changes to how Java is modelled because currently there is only a LocalClass and the predicate isLocal() only exists for Class. Similarly existing queries which only check for LocalClass would need to be updated to check for LocalInterface as well (respectively isLocal() should be moved to RefType and that predicate should then be used).
• The rules for static members were relaxed, see JDK-825432 (currently not mentioned explicitly in the release notes). This allows declaring static members in non-static enclosing types.

[rdmarsh2]

We are actively working on Java 16 support now that it's been finalised and the JDK has been released. I've asked our Java team to update you as they make progress.

[smowton]

Done in #6520 and corresponding Java extractor changes.