feat(shareBehavior): add shareBehavior and its tests

[staltz]

No description provided.

[benlesh]

This is bike-shedding, but wasn't this called "shareValue" before? Is that a better term? What would make the most sense for people new to the library? (FWIW: I found the name of "BehaviorSubject" to be essentially nonsense when I first started using Rx)

[benlesh]

Also, wasn't there a problem with shareBehavior, @staltz? Or was that only for shareReplay? (The problem being that it creates a new Subject in it's multicast)

[staltz]

This is bike-shedding, but wasn't this called "shareValue" before? Is that a better term?

It was, but we discussed here and reached a consensus to align the sharing names to their respective subjects, for symmetry:

• share uses Subject
• shareReplay uses ReplaySubject
• shareBehavior uses BehaviorSubject

To rename it to shareValue would mean also renaming BehaviorSubject to ValueSubject. I'm not contesting that actually. My brain got used to BehaviorSubject as a name, and perhaps to people migrating to v5 it would be easier to keep the same names, but I actually agree that ValueSubject would be more intuitive.

Also, wasn't there a problem with shareBehavior, @staltz? Or was that only for shareReplay?

Both shareBehavior and shareReplay "have problems" (this issue), and these tests are not covering those problems yet. So this PR here is agnostic to whatever happens to our decision regarding issue #453. When that's decided, we need to add more tests for these sharing operators.

[benlesh]

Okay, thanks for the clarification. Looking over this in more detail it looks fine. Sorry, I was going through 30+ PRs or something yesterday. LOL.

[benlesh]

merged with 97ff1ec, thanks @staltz