Extract WindowMetrics logic to WindowMetricsController

We would add some mechanisms to improve WindowMetrics performance,
which will introduce more WindowMetrics logic.
Extracting it to a separate module will make the WindowMetrics logic
easier to maintain. No logic changes.

Bug: 187712731
Test: atest WindowMetricsActivityTests WindowMetricsWindowContextTests
Change-Id: Ic35501efc4e2b73af80593f3b1911be35c2f0e48