guildMemberUpdate does not utilise partials

[MattIPv4]

Please describe the problem you are having in as much detail as possible:

With both the USER and GUILD_MEMBER partial enabled, with the GUILD_MEMEBRS intent, the guildMemberUpdate event does not fire when an uncached user/member changes their nickname. However, it does fire for a fully cached user/member.

I would expect guildMemberUpdate to be able to utilise partials, with only IDs plus the updated value being passed in the objects -- I haven't looked into it much though, so I could be wrong if Discord doesn't send any useful data about the change.

https://github.com/discordjs/discord.js/blob/b8fd3f65d964f080afb42dd37eb21a13c0d84f8f/src/client/websocket/handlers/GUILD_MEMBER_UPDATE.js

Include a reproducible code sample here, if possible:

    const client = new Client({
        ws: {
            intents: (new Intents()).add(
                Intents.FLAGS.GUILDS,
                Intents.FLAGS.GUILD_MEMBERS,
            ),
        },
        partials: ['USER', 'GUILD_MEMBER'],
    });
    client.on('guildMemberUpdate', (oldMember, newMember) => console.log(oldMember, newMember));

Update the nickname of another user in a guild that the bot is in, without that user sending any message so they are uncached. Observe no logging.

Update the nickname of yourself after having sent a message in the guild. Observe change logged.

Further details:

• discord.js version: 12.4.1
• Node.js version: 12.18.1
• Operating system: macOS 10.15.7
• Priority this issue should have – please be realistic and elaborate if possible: P2 - Would be useful considering partials help with memory performance greatly.

Relevant client options:

• partials: USER, GUILD_MEMBER

• gateway intents: GUILDS, GUILD_MEMEBRS

• other: none

• I have also tested the issue on latest master, commit hash: