fix(User): set User#bot to false if not partial

[vaporoxx]

Please describe the changes this PR makes and why it should be merged:

• Closes 12.3.0 broke the User.bot property to only be null | true not false | true like in 12.2.0 #4702

#4636 recently introduced a bug where User#bot was set to null instead of false. This is the case because it checked if the bot property was present in the data to see if it was a partial or not, however this property also does not exist for a regular user. This has been fixed by using User#partial which checks if the username property exists instead.

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.

[advaith1]

It's intended to be null, it being false was the bug. this pr undos the bug fix

[vaporoxx]

Yes, but the current bug is that it's set to null even if the user is not partial instead of false which would be expected. With this PR, partial users will still have null as the value for their .bot property but full User objects won't

[tipakA]

But it's very similar in behavior to how API doesn't send TextChannel.nsfw initially, yet library sets to false if it is not explicitly in the payload, as was done in #4593

[almostSouji]

original

It's intended to be null, it being false was the bug. this pr undos the bug fix

No, that's a misconception. The bug was introduced with the "bug fix".
If Discord does not send a field in the initial data payload which is documented to be a boolean it has to be considered false. I applied a fix to this after discussion on DAPI in #4593. The exact same principle applies to User#bot.

(I even mentioned exactly that point in my PR referenced above under "further considerations")

Now, this will lead to inconsistencies with partials, since we might falsely declare bots which we only have a partial User for as "false", however that's a caveat to swallow, imo and is regulated with "partials should be considered defunct before fetching". since the fetch then will retrieve and update the truthful true for the partial (but now completed) bot.

Has discord documented that anywhere? no
Is that majorly annoying, since we need to monkeypatch the API not sending data fields? yes
Should we still do it? probably

After some more internal discussion: discord not documenting this behavior is an absolute mess and handling it ourselves even more of an headache.

[advaith1]

Ah, I see, I assumed that it was intentional to be consistent with the API from #4702 (comment)
well we should do the same thing for User#system

[louisglen1]

The JSdoc for User#bot has not been updated to account for the changes in this PR.
Unrelated to this PR, however the same issue appears to be apparent in the JSdoc for User#system.