Extensibility Testing: Refactor

[iNinja]

Extensibility Testing: Refactor

• Refactored the ValidationError and its subclasses to align optional parameters and ensure the GetException method sets the ValidationError parameter required to provide a stack trace.
• Adjusted existing delegates to use the updated ValidationError parameters and updates the identity comparer to check for the exception's stack trace when comparing validation errors.
• Moved custom exceptions and validation errors to a specific folder for extensibility testing, and the custom issuer validation delegates file is renamed to split the other validation aspects
• Added new custom exceptions for the remaining validations
• Removed the old Audience and Lifetime extensibility tests in favour of unifying the approach using the issuer extensibility tests as a template

Note: most of the files changed are due to the updated parameter order in ValidationError and subclasses.

Part of #2711