UI changes to support time feedback

The feature is behind a release flag. It is also behind an experiment
flag so it can be trialed with Googlers before general release even
after being enabled in a release.

The feedback button only shows up if there is an intent URI configured,
which should be handled via an overlay. The design means that the intent
is potentially dependent on the manufacturer (good!), though I expect we
will suggest a standard one for GMS devices so we get feedback from a
variety of devices with different form factors / capabilities.
In this default, GMS core (Google Play Services) will handle the intent
and take the user through a feedback UI flow.

Testing:

To enable the button you need to build with one of release variants that
supports dynamic flags, e.g. trunk_food.

Then release flag:
$ adb shell device_config put location com.android.settings.flags.datetime_feedback true

It still won't work without the experiment flag:
$ adb shell device_config put settings_ui time_help_and_feedback_feature_supported true

Finally, the settings entry will launch an intent when pressed which has
to have a receiver. The receiver will be in GMS core but will be subject
to its own review / launch process. Until then, this feature will remain
quiet, biding its time.

Bug: 283239837
Test: Manual (see above)
Test: atest SettingsRoboTests:com.android.settings.datetime
Change-Id: I68798798fc0a47ae4c6755174ce509fbaee24142