Change key name "Meta" to "Action key"

1. In the modifier key remapping page, the string "Meta" should be changed to "Action"
2. We should add the default focus effect when users go into this page first time.

Demo: https://screencast.googleplex.com/cast/NTA2NjA2MzEyMjI2ODE2MHw2YjRjOTljMi0xMQ

Bug: 269981968
Test: manual
Change-Id: I481be0370166a8831bedc721751e23cee3b39703