Add more Set methods

[sync-by-unito]

Set specific methods that are needed to satisfy the SDK contracts:

• assign_difference
• assign_intersection
• assign_symmetric_difference
• assign_union
• is_strict_subset
• is_subset
• is_strict_superset
• is_superset
• intersects
• set_equals - this should return whether the two collections contain the same unique elements

[sync-by-unito]

➤ Yavor Georgiev commented:

[~simon.ulsnes] what's your take, can these be implemented?

[sync-by-unito]

➤ Simon Ulsnes commented:

Yes, those are very easy to implement. Strict sub-/superset can be implemented as just checking up front whether the size is the same, and if it is, return false.

Set-equals is also trivial.

[sync-by-unito]

➤ Nikola Irinchev commented:

This is the case if the argument is also a set - for lists and results, which may contain duplicates, the size check is not sufficient to determine whether one is a strict sub/superset of the other.

[sync-by-unito]

➤ Simon Ulsnes commented:

#4435