feat(GuildPreview): implement support for "preview" endpoint (#3965)

* feat(GuildPreview): method — fetchGuildPreview

* feat(GuildPreview): structure — GuildPreview

* feat(GuildPreview): update typings

* fix(GuildPreview): remove typedef for Features — already exists

* refactor(GuildPreview): update JSDocs & method

* feat(GuildPreview): implement DiscoverySplash function

* fix(GuildPreview): description & error handling for id

* fix(GuildPreview): misleading description, assign emojis correctly

* feat(GuildPreview): func DisplaySplash & GuildPreviewEmoji interface

* fix(Typings): satisfy TSLint

* fix(GuildPreview): toJSON - returns a value now

* feat(GuildPreview): add fetchPreview method on instance of Guild

* feat(GuildPreview): update typings

* fix: missing client constructor

* fix: typo in typings

* feat(BaseEmoji): implement BaseEmoji — parent for emoji instances

* feat(BaseEmoji): refactor - GuildEmoji extends BaseEmoji now

* feat(BaseEmoji): refactor - adjust emojis prop to BaseEmoji instance

* feat(BaseEmoji): not documented fully - GuildPreviewEmoji

* feat(BaseEmoji): update typings

* fix: remove duplicate typing properties - inherited

* fix: remove redundant methods & properties - inherited / already set

* fix: let -> const

* fix: typings - put BaseEmoji after BaseClient

* fix: remove _clone method  - redundant

* refactor(GuildPreview): emojis should be a collection

* refactor: rename base class, move relevant props there and expose roles

* fix(GuildPreview): update emojis in _patch

* fix(Typings): remove empty line, add Client#fetchGuildPreview

* feat: export GuildPreview

* fix(Typings): add GuildPreview#discoverSplash, icon, and splash

Co-authored-by: LxveFades <twitchisadeck@gmail.com>
Co-authored-by: Crawl <icrawltogo@gmail.com>
Co-authored-by: SpaceEEC <spaceeec@yahoo.com>

src/structures/GuildPreviewEmoji.js

@@ -0,0 +1,26 @@
+'use strict';
+
+const BaseGuildEmoji = require('./BaseGuildEmoji');
+
+/**
+ * Represents an instance of an emoji belonging to a public guild obtained through Discord's preview endpoint.
+ * @extends {BaseGuildEmoji}
+ */
+class GuildPreviewEmoji extends BaseGuildEmoji {
+  /**
+   * The public guild this emoji is part of
+   * @type {GuildPreview}
+   * @name GuildPreviewEmoji#guild
+   */
+
+  /**
+   * Set of roles this emoji is active for
+   * @type {Set<Snowflake>}
+   * @readonly
+   */
+  get roles() {
+    return new Set(this._roles);
+  }
+}
+
+module.exports = GuildPreviewEmoji;