Fixing some launcher model tests

> Removing static mocks and using Sandbox context instead
> Removing inheritence in LauncherModel and converting LauncherApps.Callbacks
  to a separate class. decMaker sometimes fails because of API changes in
  LauncherApps.Callbacks

Bug: 319877828
Test: atest LoaderTaskTest
Flag: N/A
Change-Id: If78b5d83595627a355b284f52d887d75fef53014
11 files changed