Add new metrics in power menu

These include,
1. An event indicating that power menu is shown.
2. An event indicating that user taps the emergency dialer icon.

Bug: 111378820
Test: manual and check the result of
'adb logcat -b events | grep sysui_multi_action'

Change-Id: I958ed1af65f559e4999517031cd80fbb1c417108