Support merging UV's that share the same vertex and are very close when applying modifiers.
This is needed to prevent UV's becoming "detached" which can happen when applying the subdivision surface modifier.
This regression was caused by [0] which removed selection threshold for nearby coordinates.
While restoring the UV selection threshold could be done - some selection operations that walk around connected UV fans wouldn't behave in a deterministic way (such as select shortest path). There are also other cases where UV's may be compared without a threshold such as tangent calculation and exporters which have their own logic to handling UV's.
[0]: b88dd3b8e7b9c02ae08d4679bb427963c5d21250