feat(FocusOriginMonitor): add support for touch events

[mmalerba]

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[mmalerba]

@devversion I stole this number from material 1, but any idea where it comes from?

[devversion]

Yeah I think the timeout is still fine. I took it from angular/material#7965 (comment)

[devversion]

Also mind exporting this variable? So the tests can use it for their setTimeout's?

[mmalerba]

@devversion I've made the change to compare event targets that you were asking for. While it is a little simpler, I believe it is less correct than what I had previously. Consider this example:

<div tabindex=1 #d cdkFocusClasses>
    <button (click)="d.focus()"></button>
</div>

Here the div will be given the cdk-touch-focused when the button is touched. This is technically incorrect, though I admit it is a very small edge case. So its a question of whether we keep the simpler almost correct solution or go with the more complicated but more correct solution.

[devversion]

@mmalerba I see. I just ran your PR locally on my end and saw the issue.

I went through the _wasCausedByTouch logic again and I'm pretty sure that we could remove the .contains check here.

Prop	Description
TouchEvent.target	Target is always type of Element and can be stored
FocusEvent.target	If the same as TouchEvent.target then it was caused by touch. Focus will only happen if the element is explicitly touched. No subtree handling necessary

This would also solve the issue you mentioned above.

[devversion]

LGTM - We had a discussion again and the current approach works fine (Miles will add a comment)

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