mesoscopic rail signals do not work

[behrisch]

"Error: stop retrieval not yet implemented for meso" triggered by MSRailSignal::DriveWay::reserve

[namdre]

meso support got broken crash was introduced by #6794

[namdre]

for the record: the rail signals still don't work because they only look at lanes (and those are empty in meso).

[namdre]

was fixed in #18027 and #18028 (with the groundwork laid in #7578 and #17842)

Some leftover work is in #18028