Enable R8 for settings

Keep constructor which is only used directly from test.

Update Proguard configuration to include information on checked
exceptions for Mockity to mock thorwn exception.

Bug: 74756073
Test: atest
com.android.settings.deviceinfo.storage.StorageAsyncLoaderTest#testRemovedPackageDoesNotCrash
Utf8ByteLengthFilterTest
Change-Id: Iae87e6647b28ee69d38bd8891df46239779c459c

proguard.flags

@@ -1,6 +1,10 @@
 # This is a configuration file for ProGuard.
 # http://proguard.sourceforge.net/index.html#manual/usage.html
 
+# Some tests use thenThrow from Mockito which require information on
+# checked exceptions.
+-keepattributes Exceptions
+
 # Keep all Fragments in this package, which are used by reflection.
 -keep public class com.android.settings.** extends android.app.Fragment