Add collection.BitSet factory object (and other cross-compatibility improvements)

[julienrf]

I’ve started with the collection.BitSet object and then found a couple other issues. I’ve added commits that address them.

In summary, this PR:

• Adds the collection.BitSet object (like in the current collections),
• Adds an overload for the updated operation on StringOps,
• Pulls up the fill and tabulate operations from SeqFactory to IterableFactoryLike. The fill method makes no sense on Set collections but … we have it in 2.12, so it’s simpler to just keep it…
• Adds an append alias for the lazyAppendAll in LazyList.