Document new `ExceptionHandlerOptions.SuppressDiagnosticsCallback` setting -- part 2 code and text for the new feature

[tdykstra]

@copilot see the comment box below
Fixes #36057

Fixes #35852

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Associated WorkItem - 488032

[tdykstra]

This Issue is a follow-up to #35852. Its main purpose is to document the new callback, SuppressDiagnosticsCallback. But we should take this opportunity to improve the coverage of IExceptionHandler, which is the context of the new callback.

• Your changes will be in ErrorHandling.md, the sections about IExceptionHandler.
• Right at the start the text should mention that there's only one method in this interface and explain how the built-in Implementation works.
• The explanation of how things work should focus on .NET 10 behavior, briefly mentioning how earlier versions differ. Starting in .NET 10, the default behavior is to suppress emission of diagnostics such as logs and metrics for handled exceptions. The default behavior can be changed by setting the SuppressDiagnosticsCallback property to false.
• Code examples:
  • Keep the two that are already there,
  • Add one that returns false to the new callback to set the default back to the way it works in .NET 8 and 9.
  • Add one that examines the context and can set the callback either way depending on context from call to call.
• Explain what happens if an exception isn't handled by any exception handler. back to the default behavior and options from the middleware. as shown in the following code example:

app.UseExceptionHandler(new ExceptionHandlerOptions
{
    SuppressDiagnosticsCallback = context => false
});

• You can also set this callback to conditionally suppress diagnostics based on the exception type or other context:

app.UseExceptionHandler(new ExceptionHandlerOptions {
    SuppressDiagnosticsCallback = context => {
        return context.Exception is ArgumentException;
    }
});

These code examples show both a simple case (always return false) and a more advanced case (conditional suppression based on exception type).

• "See also" links

• SuppressDiagnosticsCallback

• Breaking Change issue Be sure to read this To understand how the new callback works.