Introduce configuration parameter for default extension context scope

[marcphilipp]

Overview

The new junit.jupiter.extensions.testClassInstanceConstruction.extensionContextScope.default configuration parameters allows to change the default extension context scope introduced in #4062 to allow checking for compatibility issues of existing extensions without having to change their implementation.

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Definition of Done

• There are no TODOs left in the code
• Method preconditions are checked and documented in the method's Javadoc
• Coding conventions (e.g. for logging) have been followed
• Change is covered by automated tests including corner cases, errors, and exception handling
• Public API has Javadoc and @API annotations
• Change is documented in the User Guide and Release Notes