Entity_alternative table freezes/very slow with a large copy-paste

[jkiviluo]

When copy pasting e.g. 2000 entities to the entity_alternative table (with alternative_name and active status), Toolbox freezes.

Copy pasting 2000 entities in the "add entities" dialog on the other hand is fast even though it also sets the active status.

Originally mentioned in https://github.com/spine-tools/Spine-Toolbox/issues/2864