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

src/com/android/settings/bluetooth/Utf8ByteLengthFilter.java

@@ -16,6 +16,7 @@
 
 package com.android.settings.bluetooth;
 
+import android.support.annotation.Keep;
 import android.text.InputFilter;
 import android.text.Spanned;
 
@@ -40,6 +41,7 @@ import android.text.Spanned;
 public class Utf8ByteLengthFilter implements InputFilter {
     private final int mMaxBytes;
 
+    @Keep
     Utf8ByteLengthFilter(int maxBytes) {
         mMaxBytes = maxBytes;
     }