Various LocaleList cleanups

- Remove the LocaleList#getPrimary() API. It had become confusing
  after locale negotiation was completely implemented. For example,
  it could create the confusion that calling getPrimary() on the
  default locale list would provide the default locale, etc.
- Use the adjusted locale list from LocaleList.getAdjustedDefault()
  in Paints created with no locale list provided.
- Change LocaleList#get() to treat out of bound indexes from both
  negative indexes and too large indexes the same way.

Bug: 26984092
Bug: 26193251
Bug: 26834387
Change-Id: I75f77aea6b75e38793ed8477e5e5a4420d5e6d85