ShutterSoundToggle v1.2

Grey out the buttons that would change nothing

A button that stays enabled after it has done its job gives no hint of
what state the setting is in. Enable stopping the enforcement only
while it is enforced and restoring only while the value differs from
the device default, and explain on screen when the device does not
enforce the sound at all, instead of after a press.

ShutterSoundToggle v1.1

Say what a button did

A press only showed up as the status line changing, and on a device
where AudioService never enforces the shutter sound it changed nothing
at all, which looked like the app was ignoring the button. Show the
outcome of every press, explain the no-op case on screen, read the
value back after a change, and log it for logcat.

ShutterSoundToggle v1.0

Sign builds and publish tagged releases

CI signs with the public AOSP test key so that its APKs install, and
checks the fingerprint so that it can never hand out the release key's
signature. A v* tag builds with the release key from the Actions
secrets and checks that fingerprint before attaching the APK to a
GitHub release, since an APK signed by any other key cannot update an
existing install.

versionCode follows the run number so that each release can be
installed over the previous one.