WELD-1753 Introduce Weld's ImmutableSet
WELD-1753 Replace Guava's ImmutableSet usage with Weld's one
WELD-1753 Remove redundant mask. Override spliterator's characteristics.
WELD-1753 Better code reuse
WELD-1753 More changes to ImmutableSet
WELD-1753 Some more changes