feat(@angular-devkit/build-angular): add support for port 0 when using protractor

[alan-agius4]

Fixes #13129

Depends on #13292 since checkPort was changed to return a Promise instead of Observable.

[clydin]

The actual port should really be pulled from the dev server. The OS knows how to handle zero, it would be more ideal/efficient to let it do the port determination.

[alan-agius4]

@clydin, so why does the webserver has the logic to checkPort?
https://github.com/angular/angular-cli/blob/master/packages/angular_devkit/build_angular/src/dev-server/index.ts#L70

Also, the would change the return type of the builders since at the moment builders return BuildEvent.

[clydin]

We currently start the zero port search at a fixed number and changing that would be a breaking change. Ideally we should get rid of that logic in the next major and skip the port checking logic if zero is supplied. Since this is not burdened by the legacy behavior we can move directly to the ideal scenario.

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