Make ConfiguredJarList immutable

By making the Append and RemoveList methods return a new list instead
of modifying the existing list it makes the ConfiguredJarList usages
easier to reason about and safer to use, especially considering that
they are primarily used in global configuration.

Bug: 171479578
Test: m nothing
Change-Id: I102c4fb42f0c54e4ed299d2921fbf5efeb6e99b9