Consistent way to check if stream is MemoryStream

[wclr]

There is two methods I believe available now:

Check if instance of MemoryStream, not always applicable, as there may be problems with nested modules.
Check if the object has property _has present, but it is just a hacky way.

Probably need to add a more consistent method that will be officially exposed.

[staltz]

I'm open to doing this (probably exposing a nice method that internally utilizes _has or something like that), but I'm curious what's your surrounding use case for this? I haven't done this check myself yet.

[wclr]

I'm implementing HMR for cyclejs components, so there I replicate (create proxy) streams and need to know if to create with memory or not.