[flexiglass] Dual shade education tooltips.

Full stack (data, domain, and UI layers) implementation of dual shade
educational tooltips as per the latest spec.

When the user expands one of the two dual shade overlays, 5 seconds
after doing so, a tooltip will be shown to promote the existence of the
other shade.

Once a tooltip its overlay is shown for the first time for the user,
that tooltip will never be shown again.

The implementation also minimizes the number of running coroutines such
that once education is no longer needed (because an impression already
happened or because the user is not in dual shade mode), only one coroutine will remain running (namely, the one that monitors those conditions).

To turn on debug logging:
$ adb shell setprop log.tag.DualShadeEducation VERBOSE

To reset the state so the tooltips trigger again:
$ adb shell pm clear com.android.systemui

Bug: 406213664
Test: view-model level integration tests added
Test: manually verified that the correct tooltip appears on the correct
side when I expand one of the two overlays and never shown again
Flag: com.android.systemui.scene_container

Change-Id: I38e9114e4382fd04fb4d0beede4bc63a82fad244