I've read some notes about Nim0.18's GC,
are they right for Nimv2?I have some options but not sure if correct, which will
be listed afterward.
● The GC uses thread-local heap.
● The GC can hardly be shared between different dynamic libs.

I guess the latter is not correct for now with the coming of
`setupForeignThreadGc()` (not sure as I haven't tried it yet)