Show split screen dialog on the introduction and enrolling page.

Revert ag/22361082 and ag/22460413, show the split screen dialog on
the introduction and enrolling page, instead of relying on the callers
to show the dialog.

Test: atest BiometricsSplitScreenDialogTest
Test: atest FaceEnrollIntroductionTest
Test: atest SetupFingerprintEnrollIntroductionTest
Bug: 299573056

Change-Id: Ieb106a4a623ad5ca0e6eb1633413df75767bef52