Obsolete GlobalConfiguration

[angularsen]

Fixes #600 .

So it can be more easily removed in v5.

• Mark GlobalConfiguration as obsolete
• Use Thread.CurrentThread.CurrentUICulture as backing value ⚠️
• Update usages to use Thread.CurrentThread.CurrentUICulture directly

This is kind of a breaking change. Before it would initialize to CurrentUICulture upon first static access to GlobalConfiguration and that value would no longer match per-thread - but rather be globally static across threads. With this PR, it would instead match .NET's per-thread setup - which one could argue is a bug or a feature that we didn't - but since GlobalConfiguration was introduced in v4 in December and I don't think many/anyone relies on this initialize once behavior, I vote to take this in now.

[tmilnthorp]

I think we should probably be using CurrentCulture, not CurrentUICulture. At least for the number formatting. Maybe CurrentUICulture is more appropriate for the abbreviations?

I found an interesting quote here:

Often times they are both the same. But on my system they would be different: I prefer my numbers and dates in the German format, so the CurrentCulture would be German, but I also prefer all my applications in English, so the CurrentUICulture would be English.

[angularsen]

Yes, that matches how I remember it when reading up on that a long time ago. CurrentCulture for numbers, CurrentUICulture for abbreviations and other texts tied to language/culture.
However, for this PR, we can't do that change I think. Changing backing value to current thread's culture is fine I think, should not affect many - only those actively manipulating this value from multiple threads.
Changing it from CurrentUICulture to CurrentCulture sounds like would affect a lot more people, such as that german guy you mentioned.

I'm happy to address this in v5, but for this PR I think it's out of scope?

[tmilnthorp]

Agreed!