Align use of extension point

[nipafx]

Closes #479.

Proposed commit message:

Align use of extension point (#479 / #496)

If an extension needs to search for enclosing elements, there are
basically two ways to do so: 

1. Combine `BeforeAllCallback`/`AfterAllCallback` with
`BeforeEachCallback`/`AfterEachCallback`.
2. Use`BeforeEachCallback`/`AfterEachCallback` and look up enclosing
elements (e.g. via
`PioneerAnnotationUtils#findClosestEnclosingAnnotation(...)`).

We agreed on approach no. 1 since it enables the use of extensions in
setup/teardown methods. This PR aligns the use of extension points to
guarantee consistent behavior across different extensions.

Closes: #479
PR: #496

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PR checklist

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It is based on our contributors guidelines, especially the "writing code" section.
It shall help to check for completion of the listed points.
If a point does not apply to the given PR's changes, the corresponding entry can be simply marked as done.

Documentation (general)

• There is documentation (Javadoc and site documentation; added or updated)
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Contributing

• A prepared commit message exists
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I hereby agree to the terms of the JUnit Pioneer Contributor License Agreement.

[nipafx]

What's missing:

• documenting the extension scope in their respective documentations
• documenting the general approach in CONTRIBUTING.md
• checking all extensions:
  • system properties and environment variables
  • default locale and time zone
• checking means:
  • verify behavior re before/after all
  • potentially add tests for resetting

[beatngu13]

@nipafx did a rebase, addressed the remaining tasks, and wrote a commit message. ✌️

[nipafx]

Great work, thank you @beatngu13! I changed a few things - see commit messages.

[Bukama]

I like it, especially the addition in the docs 👍

[Bukama]

@beatngu13 will have a look in when he has a quite minute

[nipafx]

I think we wanted to model the tests of DefaulTimeZone after DefaultLocale before merging.

[nipafx]

At least the tests need to be aligned before this is merge-ready. Also, this conversation needs to be resolved.

[Bukama]

Merge conflict needs to be resolved

[beatngu13]

I think I did it … proposed commit message:

Align use of extension point (#479 / #496)

If an extension needs to search for enclosing elements, there are
basically two ways to do so: 

1. Combine `BeforeAllCallback`/`AfterAllCallback` with
`BeforeEachCallback`/`AfterEachCallback`.
2. Use`BeforeEachCallback`/`AfterEachCallback` and look up enclosing
elements (e.g. via
`PioneerAnnotationUtils#findClosestEnclosingAnnotation(...)`).

We agreed on approach no. 2 since it appears to be less error-prone
and cover more common use cases.

This PR aligns the use of extension points to guarantee consistent
behavior across different extensions.

Closes: #479
PR: #496

[Michael1993]

LGTM - I do have a couple nitpicks about it.

[Michael1993]

Actually, the build is platform-dependent now? How did that happen?

[beatngu13]

Actually, the build is platform-dependent now? How did that happen?

I forgot this:

junit-pioneer/src/test/java/org/junitpioneer/jupiter/DefaultTimeZoneTests.java

Lines 38 to 39 in 30cca6e

	// we set UTC as test time zone unless it is already
	// the system's time zone; in that case we use UTC+12

Apparently, the macOS job was using UTC, so the test default resulted in UTC+12. Fix:

30cca6e

[Bukama]

See my comment on the comment-question, if I'm the only one who does it wrong, see this as approved.