Added support for custom JSR-223 based formatters

[tisoft]

Added support for custom JSR-223 based formatters in Maven.

<jsr223> <!-- specify replacements using JSR223 scripting -->
  <name>Greetings to Mars</name>
  <engine>nashorn</engine>
  <script>source.replace('World','Mars');</script>
</jsr223>

Allows an end user to create arbitrary custom formatters inside the pom. Javascript is supported by the "nashorn" engine provided by the JDK. Other engines can be used, if they are in the classpath.

[tisoft]

Note: I didn't implement this for grade, since the custom step is available there. If you want this step also available in the gradle plugin, I can add it there, too.

[nedtwigg]

I think this is great, and I agree it makes sense to keep it maven-only. Only thing missing imo is that it needs a changelog entry in the root CHANGES.md too.

[tisoft]

• Updated root CHANGES.md
• Load script engine from JarState
• Added test for using a JSR-223 from a dependency

[nedtwigg]

Please merge the latest origin/main into this PR. That should fix CI, at which point I can merge and release.

[nedtwigg]

I went ahead and merged origin/main for you. Looks like the test failure is real.

https://app.circleci.com/pipelines/github/diffplug/spotless/1259/workflows/d151483f-7468-4aed-89fa-c2fcd9a2718c/jobs/7153/tests#failed-test-0

[tisoft]

I'll have a look

[tisoft]

Rebased and fixed the test failure. The new test failure seems to be unrelated.

[nedtwigg]

Want me to cut a release now, or should I wait until POM sorting gets merged too?

[tisoft]

I'll have a go at the pom sorting, no need for a new release for me.

[nedtwigg]

Released in plugin-maven 2.15.0.