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

This CL calls methods in UdfpsEnrollUtils.java to announce a11y
message. Besides, scale factor calculation and UdfpsOverlayParams.java
are removed since they are added in settingslib/.

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: I408ac6a36352aa4bfd4ac1374e3922163dbc2199