[core] Handle transition duration of 0ms for symbols

[ChrisLoer]

Fixes issue #13506.

• Setting the value to zero caused divide-by-zero errors
• Small non-zero values worked, but were unexpectedly expensive (because of requiring frequent collision detection)

Although this commit reverts the configurable duration, it leaves the "enablePlacementTransitions" flag intact.

cc @ansis @tmpsantos @brunoabinader

[ChrisLoer]

cc @tobrun

[ChrisLoer]

Actually I convinced myself we don't need to revert the configurable duration, we just need to preserve the logic that does placement at >=300ms intervals even if fading is set to happen faster. I think I was misunderstanding what I was seeing running the repro case in the Android debugger.

[ChrisLoer]

Updated this PR to just do the smaller change of handling the "divide by zero" case. The symbol fade duration still inherits from the map's "transition duration", and I verified that if it's set to less than 300ms, collision detection is still rate limited to every 300ms (although the fade duration itself is still shortened).

[brunoabinader]

Thanks @ChrisLoer 👍