Fix issue with no rounded corners on PIP

- Existing code dependend on SysUI config listeners making an extra
  density change callback when registering a config listener, but
  we should explicitly update the resources when creating the
  helper class as well

Bug: 239689748
Test: Enter pip, see it has rounded corners
Change-Id: I673e561567de91da40d02a87a4571b56794efbfe