[VL] Tight Java-C++ object binding

[zhztheplayer]

Description

PRs for #3077 will untangle codes to create a local execution context and decouple query execution from JniWrapper.

A remaining issue is that we still bind a lot of C++ objects to Java by explicit pointer transmission over JNI. We'd simplify the routine by using a JVM-native way like finalize() or weak references.

The prons if we do this:

1. Simplify JNI codes
2. (probably) The objects can be collected on-demand rather than when task ends

Since #3077 is mostly about centralizing the object management, this would be a separate topic aside but more or less related to #3077.

[zhztheplayer]

@Yohahaha I'll take this following your PRs.

[zhztheplayer]

Let's use 39a5162 's approach until it's needed to be improved.