fix(Partials): correctly set properties as nullable

[NotSugden]

Please describe the changes this PR makes and why it should be merged:
This PR changes some properties to be explicitly set to null, as they are supposed to be, from structures that can be partial

There is also a change from truthy checks to 'x' in data in the _patch methods of said structures
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
  • I've done a brief check, but it seems to all be covered by the Partial* interfaces

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.

[vladfrangu]

This PR looks 👍 however won't this be considered a bit breaking as now certain properties known to be "always present" are now "possibly present"? Also, are these changes reflected in the typings? 😅

[NotSugden]

yeah it could be considered breaking for properties like User#bot i suppose, since now it can be null, whereas before it would always default to false (although that behaviour was a bug), and i have done my best to reflect all the changes in the typings

[iCrawl]

Needs a rebase.