Rework multi battle partner data

[ShinyDragonHunter]

Description

This is my first PR so I do apologise if it isn't perfect...

This PR restructures battle partner data so they use their own array separate from gTrainers so a user isn't wasting trainer flags. Generating the party data is handled through a new CreateNPCPartyData function which generates the party based on the party flags given to the array entry with a parameter handling both a partner and a trainer, With partners being able to set their trainer name and trainer id to the party for the summary screen. Partners use the trainerPic field in the data for the back pic whilst trainer still use it for the front pic.

Here's the new array for partners with Steven's vanilla party data remade with it:

const struct Trainer gBattlePartners[] = {
    [PARTNER_NONE] =
    {
        .party = {.NoItemDefaultMoves = NULL},
    },

    [PARTNER_STEVEN] =
    {
        .aiFlags = 0, // TODO: allow partners to use their own AI flags
        .party = EVERYTHING_CUSTOMIZED(sParty_StevenPartner),
        .trainerClass = TRAINER_CLASS_RIVAL,
        .encounterMusic_gender = TRAINER_ENCOUNTER_MUSIC_MALE,
        .trainerPic = TRAINER_BACK_PIC_STEVEN,
        .trainerName = _("STEVEN"),
    },
};

static const struct TrainerMonCustomized sParty_StevenPartner[] = {
    {
        .ev = TRAINER_PARTY_EVS(0, 252, 252, 0, 6, 0),
        .iv = TRAINER_PARTY_IVS(31, 31, 31, 31, 31, 31),
        .moves = {MOVE_LIGHT_SCREEN, MOVE_PSYCHIC, MOVE_REFLECT, MOVE_METAL_CLAW},
        .species = SPECIES_METANG,
        .lvl = 42,
        .nature = TRAINER_PARTY_NATURE(NATURE_BRAVE),
    },
    {
        .ev = TRAINER_PARTY_EVS(252, 0, 0, 0, 6, 252),
        .iv = TRAINER_PARTY_IVS(31, 31, 31, 31, 31, 31),
        .moves = {MOVE_TOXIC, MOVE_AERIAL_ACE, MOVE_PROTECT, MOVE_STEEL_WING},
        .species = SPECIES_SKARMORY,
        .lvl = 43,
        .nature = TRAINER_PARTY_NATURE(NATURE_IMPISH),
    },
    {
        .ev = TRAINER_PARTY_EVS(0, 252, 0, 0, 252, 6),
        .iv = TRAINER_PARTY_IVS(31, 31, 31, 31, 31, 31),
        .moves = {MOVE_THUNDER, MOVE_PROTECT, MOVE_SOLAR_BEAM, MOVE_DRAGON_CLAW},
        .species = SPECIES_AGGRON,
        .lvl = 44,
        .nature = TRAINER_PARTY_NATURE(NATURE_ADAMANT),
    }
};

This PR also adds functionality for both trainers and partners for the rival and all a person needs to do is set the rival's name to {RIVAL} and the trainer name in-game will display the name set for the rival. By default, it's set to MAY if male and BRENDAN if female.

Discord contact info

[AlexOn1ine]

This does clear a lot of redundant code and I do like the idea to use a separate array to not waste flags but I don't see how it makes easier to create multi battles. Could you elaborate it a little bit?

[AlexOn1ine]

I know this was a conversation in discord but why does it have to be this convoluted and the macro multi_2_vs_2 can't be used instead?

[Bassoonian]

Superseded by #3592