@WillBecomeValue annotation

[zhelenskiy]

This is the discussion related to the @WillBecomeValue annotation. The current full text of the proposal can be found here.

It is proposed to add a @WillBecomeValue annotation for classes that are value-like but can't yet be value classes (multiple fields, open, etc.). It makes the compiler warn on identity-sensitive usages (===, synchronized, identityHashCode), so users can fix their code before the class actually converts and those usages become errors. Analog of Java's @jdk.internal.ValueBased (JEP 390).