stream: standardize async initialization

[ronag]

Some streams (e.g.fs and net) need to first asynchronously create resources before they can perform any work. Currently this is implemented in the different stream implementations which both makes things more difficult and error prone (e.g. 'open' and 'ready' are emitted after 'close'). I suggest we provide a standardized way of achieving this.

This would allow further simplification and improved consistency for various stream implementations such as fs and net stream.

I propose the following API for this:

• a stream._construct(cb) endpoint (similar to _destroy(cb)).
• a stream.ready property indicating whether the stream is ready (currently this is called pending in some implementations). Including readableReady and writableReady accessors.
• a 'ready' event (currently this is called 'open' in some implementations).

See, nxtedition#2 for proof of concept.

[ronag]

I suggest in order to land this we first update either net or fs to as far as possible use "standardized" streams (e.g. #29048) and then try to apply this suggestion there to prove the concept.

[ronag]

Here is a proposal implementation. Don't think I can get much further without some feedback.

nxtedition#2

[ronag]

This has landed.