Add udfps/ and support a11y for the udfps enroll view.

This CL:
1. Adds udfps/ in settingslib/ for sharing methods.
2. Moves scale factor and UdfpsOverlayParams.java to settingslib/.
3. Adds an accessibility view for fingerprint sensor annoucement.

Test: atest UdfpsControllerOverlayTest
Test: manually tested on device:
      Turn on talkback and turn this flag on via adb command
      adb shell setprop
        sys.fflag.override.settings_show_udfps_enroll_in_settings true
Bug: 186873966, 260617060
Change-Id: I083ccfccb435ad5baf29afd377098dd127a63f80