Collect wildcards in statements before splitting

[kstrauser]

In Statement.split, the list of actions wasn't being deduplicated, going through wildcard matching, etc. before being split. The end result was that some of the intermediate statements were by themselves too big to be packed into a single policy. It went something like this:

1. Calculate the length of the (properly cleaned up) statements.
2. Use that to figure out how many split up statements to yield.
3. Now divide the un-cleaned-up statements into that many statements.

Oops! Since the un-cleaned-up list is typically a lot bigger than the canonicalized output, some of those child statements may be a lot larger than expected.

This fixes that and refactors just a little bit. All of the test changes are renames due to adjust for the refactoring, plus running a newer version of Black.