**Only one functional change**
* Fixes a bug in LogFactory where `Warning` is being logged as `Information`
Non-functional changes:
* Updates/Fixes copyright headers
* Removes namespace scopes for core files.
View with [whitespace off](https://github.com/modernuo/ModernUO/pull/1187/files?w=1).
* Optimizes OrderedHashSet using the learnings here: https://github.com/dotnet/runtime/issues/10050
* Removes ValueCollection since it was a relic from the conversion of the OrderedDictionary
* Centralizes throw strings.
* Adds pooled ordered hash set (but doesn't use it)
Closes#448
