Before, partial bridges were calculated. For each of these an angle
has been choosen and after that all the bridges have been merged.
Becouse of the merge a single angle had to be picked.
The first angle that the algorithm has stumbled upon has been picked,
resulting in sub-optimal bridging directions.
Now the partial bridges are calcualted, then merged and then
the angle is decided over the whole merged bridge.
This approach at least ensures that the orientation is the best possible
for the merged bridge.
This enables addition of other expansion zones in the future.
For example to make sure bridges are anchored properly even
if there is top fill next to them.
Split the function expand_bridges_detect_orientations into
multiple functions. And allow any number of expansion zones
by using a vector instead of explicitly listing the
parameters.
