Feature: Alternative linkgraph colour schemes

[2TallTyler]

Motivation / Problem

Per #9168:

According to the NHS, about 1 in 12 men and 1 in 200 women are red/green colourblind.

The linkgraph colours which show if a route is overloaded, saturated, or unused currently use a red-green colour scale. Additionally, the green "saturated" colour matches the temperate grass and is quite difficult to see.

Description

In conversations in #9513 and on Reddit, a number of colourblind users stated their preference for other information besides colour to convey information and for the game to offer them a choice of colour schemes.

I think #9760 adds the other information, and this commit adds more colour scheme choices. Specifically, it upstreams a JGRPP commit to add three additional colour schemes:

• Green to red (original)
• Green to blue
• Grey to red
• Greyscale

Closes #9168
Alternative to #9513

Limitations

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 touches english.txt or translations? Check the guidelines
• 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

Typo is typo :)