Please describe the changes this PR makes and why it should be merged:
We have methods like ChannelsAPI#createMessage(), InteractionsAPI#reply(), InteractionsAPI#updateMessage(), etc. where the body parameters are of types that intersect with objects. That means we have to do this as they are not exported:

const payload: Parameters<ChannelsAPI["createMessage"]>[1] = {
    allowed_mentions: { parse: [] },
    embeds,
    files,
};

if (content) {
    payload.content = `${stamp} ${content}`;
}

The reason for this is because content is conditionally present. We cannot type this as RESTPostAPIChannelMessageJSONBody because files is not there. This is a @discordjs/core-specific type.

Doing Parameters<ChannelsAPI["createMessage"]>[1] is not ideal as when the library introduces minor or major changes, parameters may shift which results in yet again browsing the source code to see the intersected types. These types should be exported for ease.

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating