Add dynamic predicate support (Kotlin, Scala, others)

[bsideup]

At S1P, we discussed with @elizarov the possibility of adding BlockHound integration to Kotlin:
Kotlin/kotlinx.coroutines#1031

One of the major blockers was a lack of an API to dynamically decide whether thread is blocking or non-blocking since, in Kotlin, they change it dynamically.

This PR adds a new API to mark thread as "dynamic", which means that the blocking check should call threadPredicate once again before reporting the blocking call.

Example usage:

b.aaDynamicThreadPredicate(DynamicThread.class::isInstance);

b.nonBlockingThreadPredicate(p -> p.or(thread -> {
    return thread instanceof DynamicThread && ((DynamicThread) thread).isNonBlocking;
}));

where DynamicThread#isNonBlocking is a field that reflects the current "mode".

[bsideup]

@elizarov could you please take a look at this new API and tell us if this will be sufficient for Kotlin? Thanks!

[elizarov]

@elizarov could you please take a look at this new API and tell us if this will be sufficient for Kotlin? Thanks!

Looks good to me!