Add ContrastDialog class and tests, activity version

Creates the SystemUIDialog class for contrast, as well as the intent
ACTION_SHOW_CONTRAST_DIALOG and a helper class that listen to the intent to
open the dialog.

Bug: 266071578
Test: atest ContrastDialogTest
Change-Id: I3c5f25ccd99d5b8875a8fa1fdb9f24ef4886c72b
14 files changed