Relocate @API to a stand-alone module

[sbrannen]

Overview

The @API annotation may better serve the community at large if it is moved from junit-platform-commons to a stand-alone module.

Related Issues

• Introduce tools for @API annotation processing #144
• Make @API public to allow Extensions and TestEngines to adopt API semantics #317
• Make @API annotation available via Java reflection #375

Deliverables

• Refactor the @API annotation so that it has the following attributes:
  • status: Status (used to be value)
  • since: String (version the status was last changed, e.g. "5.0.0", defaults to "")
  • consumers: String[] (list of package patterns for intended consumers, defaults to {"*"})
• Rename Status constants to align with industry standards for enum constants.
• Set since attribute across the JUnit 5 code base.
• ❌ Set consumers attribute across the JUnit 5 code base.
  • to be addressed in Set @API consumers attribute across the code base #1054
• Move @API to a stand-alone project on GitHub.
• Use @API from the @API Guardian project and delete @API from junit-platform-commons.

[sbrannen]

Currently slated for 5.0 M5 in order to be discussed amongst the team.