Enhancement: Speed icon overlay position for monorail

[originalfoo]

From #1322 (comment) :

Works for monorail (derives from TrainTrackBaseAI) although overlay should be one "level" higher (where 80)

[originalfoo]

An additional enhancement for this would be to show monorail sub-icon to make it obvious which icons relate to monorail track.

Something like that already done when editing speeds for lanes on a road that contains monorail track (although we could make the sub-icon a lot smaller):

[krzychu124]

Cool idea! Love it

[originalfoo]

Is it just monorail where icons are appearing on ground or all elevated networks?

[krzychu124]

Yup. for other networks they seem to be rendered correctly

[originalfoo]