Closes #8842 (alternative of)

Motivation / Problem

See #8647.

• OpenTTD put front and back sprites in the same sprite-order position. So both front and back sprites glitches with vehicles.
• Some constants in src/table swapped front/back sprites. But this was not noticeable before due to the first issue.

In general road catenary consists of 5 parts:

• 4 pillars in N, W, E, S corners
• wires on top.
  But the specs combine them into two sprites, which does not work... west and east pillars are sometimes in front of, sometimes behind vehicles.

Description

The spec seems to be:

• Back sprite: N, W and E pillars
• Front sprite: S pillar and wires.

This PR splits the back sprite into 3 sprites accordingly and draws it in 3 separate bounding boxes, so that W and E pillar are drawn correctly.

Limitations

N/A

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
• This PR affects the save game format? (label 'savegame upgrade')
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
  • The compatibility wrappers (compat_*.nut) need updating.
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
  • PR must be added to API tracker