Bridge speed should take precedence over special cases like small perimeter speed

[jschuh]

This should fix issue #4130 where the small perimeter speed is used instead of the bridge speed. I originally ran into this bug when trying to improve the overhangs on the 3DBenchy door arches (because small perimeter speed was erroneously applied to the curved part of the overhangs).

The change itself is extremely simple. It just always prioritizes the bridge/overhang role over any special-case speed that may be supplied for an extrusion. That seems like the right solution, since generally the bridge/overhang role seems to take priority over other roles elsewhere in the code.

[jschuh]

@bubnikv, this is a very small fix that seems like I trivial "yes or no" situation. Currently the small perimeter speed gets used for a bridge that's a small perimeter. That seems wrong, so the patch flips this, and will use the bridge speed instead in that case.

[mbbill]

Google brought me here when searching for solutions for the same issue. So prusa devs please consider merging this PR! It really helps improving the overhang quality.

[jschuh]

This change seems redundant with the new dynamic overhang speeds and cooling features in 2.6. But, it does still seem like the right default when either of those are disabled, so I figure I won't close it just yet.