feat(shareReplay): added 'disconnect' feature

[Malvolio]

Description:
Updated shareReplay to support 'disconnect'. That is, when the refCount drops to 0, the buffer can (optionally) be dropped, and then, upon the next subscription, re-subscribes to the source.

Rather than adding another parameter, a config-object interface has been added. For compatibility, the old parameters still work, but the disconnect option can only be reached with the config option, so shareReplay(3) is equivalent to shareReplay({ bufferSize: 3}), but you might instead want shareReplay({ bufferSize: 3, disconnect: true}).

Related issue (if exists):

This is in response to issue 3722.

[cartant]

The problem with shareReplay has been addressed in #4059 - but that PR has not yet been merged.

[Malvolio]

The problem with shareReplay has been addressed in #4059 - but that PR has not yet been merged.

Haha, I was talking to Ben Lesh and he suggested I make this change. I guess he forgot about that PR.

[coveralls]

Pull Request Test Coverage Report for Build 7820

• 32 of 32 (100.0%) changed or added relevant lines in 1 file are covered.
• 5 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.2%) to 97.038%

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Files with Coverage Reduction	New Missed Lines	%
src/internal/observable/fromPromise.ts	1	87.5%
src/internal/observable/fromIterable.ts	2	95.24%
src/internal/observable/fromObservable.ts	2	83.33%

Totals
Change from base Build 7749:	0.2%
Covered Lines:	5799
Relevant Lines:	5976

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💛 - Coveralls

[cartant]

Closing this in favour of #4059