the layout of `immut/array`

[bobzhang]

Background Following the name scheme https://github.com/moonbitlang/core/pull/2632, either we change the layout to immut/persist_array or simply move this to moonbitlang/immut/vector. The issue is that immutable vector is not of much use but requires lots of maintainance overhead And

But

Therefore

[hackwaly]

This raises a new question: Should we migrate to Java's name convention for data structures? Like TreeMap, SkipListMap...

So immut/array goes to immut/hamt_array?