Initial screenshot tests for bubbles

Add screenshot test for bubble education view.
The new test is added to a multivalent directory, but only on device
tests are currently included. Will have to add robolectric separately.

ABTD: https://android-build.googleplex.com/builds/abtd/run/L56200030004774038

Flag: TEST_ONLY
Bug: 342417102
Test: atest WMShellMultivalentScreenshotTestsOnDevice
Change-Id: I4275291b7b6758edb9bc5bc249861f421dab7f8f