Get rid of 'synchronized (String.intern())'

Genius and Netvirt are using a very funky locking scheme, which is precisely:

String foo; // related to what is being processed
synchronized (foo.intern()) {
    // ...
}

From software design perspective, this is bonkers, as this synchronizes with any entity performing this same thing (or accidentally uses synchronized(String)) – leading to potential collisions and preventing reasoning about locks.

From performance perspective, this is purely abysmal, as String.intern() is forcing a round-trip to the JVM level, cannot be optimized and is slow – as detailed in https://shipilev.net/jvm-anatomy-park/10-string-intern/ .

This needs to tackle only hiding this monstrosity behind an API, not with a complete migration of netvirt code to some other locking scheme.