Documentation for Reset should state that it returns the previous RNG seed

[fingolfin]

Some code even seems to rely on that.

Might be a good idea to verify all implementations do this (I am aware of only one implementation outside of GAP itself, namely in the io package).

[jackschmidt]

I believe this was fixed in #4438

I checked through the packages on an installation of GAP 4.11.1 (ubuntu 20.10) and only found three instances:

• 👍 xgap defined a Reset operation on a different type of object (text selection user interface object)
• 👍 orb defined a Reset operation on a different type of object (product replacer)
• 🤷 io defines a Reset operation on a IsRandomSource, but it does not do anything since the random source is not meant to be reproducible. It does not return any value, but I don't think there is a sensible value to return.

None of them allow setting a "seed" or anything like that, so I don't think there is any danger of confusion.