+ Added missing androix libraries to LOCAL_STATIC_ANDROID_LIBRARIES.
+ Added keep class statements for androidx and messaging classes.
+ Deleted Assert.isEngBuild call (this package is the last user of that method).
+ Added import statements for androidx classes.

Test: manual - Tested the messaging UI. Ran the following tests on Pixel phone.

$ make -j 40
$ make messagingtests -j
$ find out -name "messaging*.apk" -print -exec ls -l {} \;
-rw-r----- 1 rtenneti primarygroup 733809 Jul  9 17:42 out/target/product/bonito/testcases/messagingtests/arm64/messagingtests.apk
-rw-r----- 1 rtenneti primarygroup 10799132 Jul  9 18:34 out/target/product/bonito/product/app/messaging/messaging.apk

$ adb install -r -d -t  out/target/product/bonito/product/app/messaging/messaging.apk
$ adb install -r -d -t  out/target/product/bonito/testcases/messagingtests/arm64/messagingtests.apk
$ adb shell am instrument -w com.android.messaging.test

com.android.messaging.datamodel.BindingTest:.......
com.android.messaging.datamodel.BitmapPoolTest:....
com.android.messaging.datamodel.ConversationListTest:.
com.android.messaging.datamodel.DataModelTest:...
com.android.messaging.datamodel.FrequentContactsCursorBuilderTest:...
com.android.messaging.datamodel.MemoryCacheManagerTest:.
com.android.messaging.datamodel.ParticipantRefreshTest:..........
com.android.messaging.datamodel.action.ActionServiceSystemTest:.....
com.android.messaging.datamodel.action.ActionServiceTest:..
com.android.messaging.datamodel.action.ActionTest:.....
com.android.messaging.datamodel.action.GetOrCreateConversationActionTest:.
com.android.messaging.datamodel.action.ReadWriteDraftMessageActionTest:......
com.android.messaging.datamodel.data.ConversationMessageDataTest:...
com.android.messaging.datamodel.data.ConversationParticipantsDataTest:.
com.android.messaging.datamodel.media.ImageRequestTest:..
com.android.messaging.datamodel.media.MediaResourceManagerTest:.....
com.android.messaging.ui.CustomHeaderViewPagerTest:.
com.android.messaging.ui.MultiAttachmentLayoutTest:...
com.android.messaging.ui.attachmentchooser.AttachmentChooserFragmentTest:.
com.android.messaging.ui.contact.ContactListItemViewTest:....
com.android.messaging.ui.contact.ContactPickerFragmentTest:......
com.android.messaging.ui.conversation.ComposeMessageViewTest:..
com.android.messaging.ui.conversation.ConversationActivityUiStateTest:....
com.android.messaging.ui.conversation.ConversationFragmentTest:..
com.android.messaging.ui.conversation.ConversationInputManagerTest:.....
com.android.messaging.ui.conversation.ConversationMessageViewTest:...
com.android.messaging.ui.conversationlist.ConversationListFragmentTest:...
com.android.messaging.ui.conversationlist.ConversationListItemViewTest:....
com.android.messaging.ui.mediapicker.AudioRecordViewTest:.
com.android.messaging.ui.mediapicker.CameraManagerTest:......
com.android.messaging.ui.mediapicker.GalleryGridItemViewTest:.....
com.android.messaging.ui.mediapicker.MediaPickerTest:..
com.android.messaging.util.BugleGservicesTest:.
com.android.messaging.util.YouTubeUtilTest:.
Test results for InstrumentationTestRunner=.........................................
.........................................
...............................
Time: 9.903

OK (113 tests)

Change-Id: If8fd8036791027739eb9bbb1d3849a46211a5137