Fetch package context only once per package

Since we're caching the result here, it makes sense to only make this
call the first time.

Bug: 375855663
Bug: 371174789
Flag: android.app.notifications_redesign_app_icons
Test: caching still works
Change-Id: Ic48ecc7648ffe3996a360cfbe4dc0ed0e550653d
1 file changed