feat(Activity): add missing fields

[advaith1]

Please describe the changes this PR makes and why it should be merged:
Adds id, platform, syncID, sessionID, and buttons to the Activity object (discord/discord-api-docs#2219)

wasn't sure if I should do something for ClientPresence because bots can't send these, but it seems to already have code to handle many properties that bots can't send [msg]

Status

• 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

Semantic versioning classification:

• This PR changes the library's interface (methods or parameters added)
  • This PR includes breaking changes (methods removed or renamed, parameters moved or removed)
• This PR only includes non-code changes, like changes to documentation, README, etc.

[kyranet]

Waiting for the linked PR to land first, but if there are no further changes, LGTM.

Stale

[advaith1]

@Vaporox all the other ones use ||, why make these different? probably won't actually make a difference here

[kyranet]

@Vaporox all the other ones use ||, why make these different? probably won't actually make a difference here

Because we landed requirement for Node.js v14 (which implements ??) fairly recently, and we haven't refactored all the eligible ||s yet.

[advaith1]

So will we use ?? as the default going forward?

[kyranet]

So will we use ?? as the default going forward?

That's correct.

[advaith1]

oh looks like syncID was already there but undocumented (in djs and discord) and doesn't default to null 🤔 should I remove the old one?
https://github.com/discordjs/discord.js/pull/4984/files#diff-72d7646d708e843ab070501124748d67961184ff3497db3f56dd5e6ac1f2ed92R237

[SpaceEEC]

Good to go, once the upstream PR is merged.