Drop stale activity configuration updates.

This CL introduces sequence number to activity configurations and use
that to compare their staleness. Always use the last reported activity
configs for Activity#onConfigurationChanged() and drop all requests
that are older than the processed one.

Fixes: 120189873
Test: Manually verify that number of configuration changes drops during
drag-resizing with a crafted app that needs 250ms to perform one
configuration change. go/wm-smoke too.
atest FrameworksCoreTests:ActivityThreadTest
atest WmTests:ActivityRecordTests

Change-Id: Ie0fd15458517470542a689b51283f4d1ed2ad4cc