Scoped value formatters about fluentassertions HOT 5 OPEN

I like the proposal of having scoped formatters 👍

As the signature is Formatter.ToString(object value, FormattingOptions options = null) placing the scoped formatters on FormattingOptions might be a good place?

When retrieving all formatters in Formatter.Format it will then search in scoped custom formatters, static custom formatters and lastly static default formatters.

Perhaps we should also move the current Formatter.CustomFormatters to FormattingOptions?
This should be doable without introducing any breaking changes, by forwarding the existing AddFormatter and RemoveFormatter.
The statically set custom formatters will then be set on the static AssertionOptions.FormattingOptions and the scoped ones will be set on AssertionScope.FormattingOptions.

To set a scoped formatter you'll only have to do

using var scope = new AssertionScope();
scope.FormattingOptions.AddFormatter(new MyCustomFormatter());

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That sounds like a great idea. Let's go for that.

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Maybe scope.UsingFormatter(new MyCustomFormatter()) is nicer?

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It is also an option, this way collection of formatters could be internal.

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I'm fine with that. What about you @jnyrup ?

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