feat: remove datastores and implement Managers

[RDambrosio016]

Please describe the changes this PR makes and why it should be merged:
This PR completely removes DataStores, and it implements Managers. The reasons for this change are highlighted in #3485, and this pr mostly implements it.

Testing

Due to the inherent breaking nature of this PR, it is not completely testable by one person. if you would like to aid in testing this pr, simply install the branch with:
npm i git://github.com/RDambrosio016/discord.js.git#remove-datastores. If you encounter any weird behavior or errors, please either comment below, or ping me on the discord server (@BorgerKing#1856).

The main focus of the PR is completely separating API and cache for data models.

This allows us to:

• Easily swap out API methods.
• Easily extend Managers.
• Easily swap out cache types.
• Separate API and cache methods so as not to have weird overwrites on various managers.

Future plans

This pr easily allows us to give users control over caching strategies through dependency injection. Users will extend collection and provide it to a helper class similar to Structures which the managers will use to get the right collection. In addition to this, bans will be made into their own manager, this will centralize the methods so as not to have them in various managers and structures.

Misc changes

• Managers of any kind are no longer iterable.
• Managers do not have a Symbol.species of Collection anymore.
• The BaseManager class is abstract unlike DataStore.
• Neither the BaseManager class, nor standalone managers extend Collection.
• Collection methods are no longer overwritten with API methods due to the separation of purposes.
• Multiple properties on stores have been documented in managers, e.g. MessageManager#channel.
• MessageStore#remove() has been renamed to MessageManager#delete()

Managers!

Abstract:

DataStore => BaseManager

Extends BaseManager:

GuildChannelStore => GuildChannelManager
GuildEmojiStore => GuildEmojiManager
GuildMemberStore => GuildMemberManager
MessageStore => MessageManager
PresenceStore => PresenceManager
ReactionStore => ReactionManager
GuildStore => GuildManager
ReactionUserStore => ReactionUserManager
UserStore => UserManager
RoleStore => RoleManager

Standalone (cache is a getter):

GuildMemberRoleStore => GuildMemberRoleManager
GuildEmojiRoleStore => GuildEmojiRoleManager

todo

• Rethink if Standalone stores should/could be reworked to extend BaseManager.
• Check over typings to see if they are fully correct.
• Overall testing.
• Test if docs work fine.
• Change jsdoc to remove references to stores/ use managers properly

Status

• Code changes have been partially tested against the Discord API.
• I know how to update typings and have done so.

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.

This PR includes significant breaking changes to both how users interact with cache, and how internals interact with the cache. It also renames some methods such as MessageStore#remove().

[appellation]

Initial, obvious typos/nits

[amishshah]

Really great PR! It achieves the points set out in #3485. Most of my complaints are just nitpicks over documentation conventions, I found very few logical errors 😄 🎉

• Some inconsistencies with capitalisation of data structures
• Some descriptions include "the cache of this Manager" whereas others include the specific structure, e.g. "the role cache of this Manager"

[amishshah]

Just some minor corrections I have for the docs

[Jyguy]

message.reactions.clear(); of line 16 in src/client/actions/MessageReactionRemoveAll.js should be message.reactions.cache.clear();