Add ESCAPE key to dismiss Overview

This CL adds the functionality of escape key to Overview. It dismisses Overview when the esc key is pressed.
When Overview is showing a Modal Task, it will return to Overview state instead of the Normal state.

Fix: 315283507
Flag: N/A
Test: TaplTestsQuickstep
Change-Id: I02e02f623d9a4aad1c2d6188fdea4e3fc4f96d64