Add new Table operations

[Clashsoft]

Add the following new table operations for parity with generated tables, as suggested by @azuendorf:

• forEach as a shorthand for toSet().forEach / stream().distinct().forEach.
• get(int i) for getting the value in the ith row of the current column.
• <S extends T> Table<S> filterAs(Class<S> type), which filters by instanceof and also returns a new table of the correct type.