GetUnitsSelectedAll and maybe SyncSelections/EnumSelectedUnits should not be used in trigger conditions

[tdauth]

There is a comment in GUI triggers for GetUnitsSelectedAll which says that and it can lead to weird deselection bugs.

[WaterKnight]

GetUnitsSelectedAll uses SyncSelections, which is a wait, in order to ensure it returns the same value on different clients. Waits are not supported in trigger conditions.

[tdauth]

Then this should be commented for both functions in jassdoc.

[tdauth]

I would also mention for SyncSelections that it can cause a major lag when called too often which was confirmed here: https://www.hiveworkshop.com/threads/selections-and-desyncs.244932/#post-2451234

and in my own map.