mat-tab: focuschange is not working with keyboard

[lokeshdaiya]

Bug, feature request, or proposal:

focusChange event of mat-tab component is not working with keyboard strokes.

What is the expected behavior?

focusChange event should work with keyboard strokes.

What is the current behavior?

focusChange event is working with mouse but not with keyboard.
When user change focus using mouse then it call method assigned to focusChange while with keyboard its not.

What are the steps to reproduce?

https://stackblitz.com/edit/angular-mat-tab-focuschange

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

Keyboard accessibility

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

angular: 6+
material: 6.3+
browser: chrome

Is there anything else we should know?

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