Updated the ActivityTypes to match the documentation

[Gamer153]

Added the COMPETING type, removed the WATCHING type and changed the order to match the documentation.

[JnCrMx]

Hmmm... It seems like the SDK is not up-to-date with the documentation.

The latest discord_game_sdk.h still defines the ActivityTypes as

enum EDiscordActivityType {
    DiscordActivityType_Playing,
    DiscordActivityType_Streaming,
    DiscordActivityType_Listening,
    DiscordActivityType_Watching,
};

This seems to be an issue on Discord's side and you might wish to report it in https://github.com/discord/gamesdk-and-dispatch or https://github.com/discord/discord-api-docs. I sadly don't have time for that now.

Also, the new enum values now skip 3 (possibly in order to not break old versions):

Playing | 0
Streaming | 1
Listening | 2
Custom | 4
Competing | 5

(https://discord.com/developers/docs/game-sdk/activities#data-models-activitytype-enum)

In order to reflect this in Java we need to add one "spacer" element to the enum (at the place where WATCHING was) or we get wrong values (e.g. COMPETING instead of CUSTOM).
We might name this spacer either UNKNOWN/REMOVED/DEPRECATED/etc. or just keep WATCHING and add an @Deprecated annotation (maybe together with one sentence of documentation) to it.

To be honest I'm not really sure about this COMPETING because I've never seen it "in the wild" before. But adding it probably won't hurt.

If you add this spacer value to the enum, I'll gladly merge this. Thank you for contributing :D

[Gamer153]

I added the spacer value (I just called it UNUSED), and I'm going to report it to the discord repos.
I hope the changes are ok now.

[JnCrMx]

Yes, it looks fine now and my test runs without problems.

I will include some other new features in the next few days (there now seems to be an instance property in DiscordActivity) and then make a new release (unless you need those changes immediately, then I will do the release right now, no problem).

Thank you again for contributing :D