feature: Add method to clear guild user cache (#1767)

* Add method to clear a SocketGuild's user cache

* Add optional predicate

* Compress overload to be consistant

* Fix global user not clearing (may cause other issues)

* Remove debug code and add param documentation

* Standardise doc string

* Remove old hack-fix

* Rename new method for consistency

* Add missing line to reset downloaderPromise

* Undo accidental whitespace changes

* Rider better actually keep the tab this time

Co-authored-by: Quin Lynch <49576606+quinchs@users.noreply.github.com>

src/Discord.Net.WebSocket/ClientState.cs

@@ -115,7 +115,7 @@ namespace Discord.WebSocket
             if (_guilds.TryRemove(id, out SocketGuild guild))
             {
                 guild.PurgeChannelCache(this);
-                guild.PurgeGuildUserCache();
+                guild.PurgeUserCache();
                 return guild;
             }
             return null;
@@ -140,7 +140,7 @@ namespace Discord.WebSocket
         internal void PurgeUsers()
         {
             foreach (var guild in _guilds.Values)
-                guild.PurgeGuildUserCache();
+                guild.PurgeUserCache();
         }
 
         internal SocketApplicationCommand GetCommand(ulong id)