Only override embedded activity locale if source package lookup yields locales to match

Calling Configuration#setLocales also sets the text direction for the containing Activity. If we pass an empty LocaleList to this method, then we lose the intended text direction for its locale. So this change will only override the target (embedded) Activity's locales if our package lookup for the host yields a populated LocaleList to provide.

Bug: 277363604
Test: Verified on Pixel devices in Settings app

Change-Id: I8bcdab0737c18f861f74a8f9bd2d15043359e27b