This changes the implementation for `Collection.difference(from:)` to
use a linear-space complexity variation of the same Myers algorithm. The
new version is similar in execution time to the existing one, but should
alleviate memory pressure when diffing collections where the number of
differences approaches the size of the collection. While the new
algorithm returns a set of changes that is the same size as the previous
version, the specific changes are not guaranteed to be the same.
rdar://155829876
Enabling both of these despite the long runtime so that I can get an
accurate measure of the change with the new diffing implementation.
After #83212 is merged I will disable these large benchmarks again.
