Use safe icon when building unavailable slices.

And move ic_a11y_generic from mipmap to drawable. IconCompat doesn't
support mipmap.

Bug: 118691898
Test: robotests
Change-Id: I6799f3d31d2c5654319e5a97bf8ca14992e785a7

src/com/android/settings/accessibility/ShortcutServicePickerFragment.java

@@ -258,7 +258,7 @@ public class ShortcutServicePickerFragment extends RadioButtonPickerFragment {
         public Drawable loadIcon() {
             final ResolveInfo resolveInfo = mServiceInfo.getResolveInfo();
             return (resolveInfo.getIconResource() == 0)
-                    ? getContext().getDrawable(R.mipmap.ic_accessibility_generic)
+                    ? getContext().getDrawable(R.drawable.ic_accessibility_generic)
                     : resolveInfo.loadIcon(getContext().getPackageManager());
         }