Add `completed` event for stepper / steps

[olman21]

Bug, feature request, or proposal:

Proposal

What is the expected behavior?

Optionally allow the consumer define if it wants to auto-advance an step when it completes (by using [completed] step property)

What is the current behavior?

Nothing happens as soon the step is marked as completed

What is the use-case or motivation for changing an existing behavior?

Use Observable based state such as NgRx stores, and in a more functional way allow set the stepper navigation based on state, now I have to subscribe to store and call navigation via an stepper instance in order to handle steps advance, too imperatively and also results in a awful timing issues because when stepper.next() is called and [completed] property update is on its way nothing happens.

Is there anything else we should know?

I'm willing to implement such feature. No breaking changes would be introduced.

[josephperrott]

It seems reasonable and if it can be done in a non-breaking way I am sure we would welcome the contribution.

@mmalerba to confirm.

[mmalerba]

I assume you mean an output (completed) rather than an input [completed] correct? That seems like a reasonable feature to me