Track Environment fields in heap snapshot?

[joyeecheung]

At the moment, the Environment fields are not tracked by the heap snapshot (unless they are referenced by some other objects that implements the MemoryRetainer interface) - for example, you can't see any of the AliasedBuffer in the Environment when looking at a heap snapshot taken after bootstrap. Considering the amount of things we attach to the Environment, it should be pretty useful to track those fields in the heap snapshot instead of keeping them invisible for no particular reason.

I am thinking about having Environment implmement MemoryRetainer, are there any concerns around having it inherit from an abstract class? (considering this is semi-exposed to embedders).

[joyeecheung]

cc @nodejs/embedders