Improve documentation of connectPolygonsAlongBridge
Improve documentation of connectPolygonsAlongBridge

Some of it needed updating. Some of it was just short or missing.
Not all off-by-one errors are fully documented. They are also very hard to explain, and very numerous. It's hard to figure out what all of the < or > need to be, or why you subtract one if iterating backwards, etc.

Contributes to issue CURA-7828.

Ultimaker/CuraEngine,Ultimaker/CuraEngine