Close #19870: Make new colours compatible with UI themes

[Gymnasiast]

This refactors the usage of COLOUR_FLAG_* to a new struct with a field for colour and a field for flags. This frees up the upper bits, which were previously clashing with any colours with ID >= 32.

Future refactors left out of this PR:

• Also refactor out the flags in the drawing engine
• Change colour_t to an enum (requires this PR and the refactor mentioned above)

[733737]

does this allow the colors to be used for ride names?

[Gymnasiast]

does this allow the colors to be used for ride names?

No, that’s a different set of colours.

[AaronVanGeffen]

Nice refactor, and good to have the extra colours exposed through the themes API. Things appear to be working properly as well.

I wonder about the serialisation aspect of the implementation, though. Like before, colours are serialised to integer numbers, just longer ones. For example:

{
    "entries": {
        "WC_CHEATS": {
            "colours": [
                257,
                19
            ]
        },
        "WC_CLEAR_SCENERY": {
            "colours": [
                280,
                24,
                24
            ]
        },

I'm wondering whether it would be better to take this opportunity to separate flags from colours as well, e.g.:

{
    "entries": {
        "WC_CHEATS": {
            "colours": [
                1,
                19
            ],
            "flags": [
                1,
                0
            ]
        },
        "WC_CLEAR_SCENERY": {
            "colours": [
                24,
                24,
                24
            ],
            "flags": [
                1,
                0,
                0
            ]
        },

It would be even better if everything used (string) constants, but I think that's overkill for a config that few people modify by hand. I think extracting the flags out would be a nice middle ground, though.

[Gymnasiast]

Stuff left to do:

• Use colour names in theme JSON
• Update plugin API to use something similar