Phase 3 Meta Issue - Fix issues with new Elixir/Java Versions

[joshuataylor]

Investigate test breakages

Unable to load JUnit4 runner to calculate Ignored test cases
Is coming up in some tests, figure out why

Support new syntax

Elixir has some new syntax for mix.exs, such as git, which throws an error. Investigate the issue tracker for bugs submitted like this. (I've downloaded all the issues and use ripgrep, which is a nice solution.).

Support HEEx

Investigate effort to support HEEx is what Phoenix uses for their LiveView template.

Support Junit5

Investigate if supporting Junit5 is easyish.

With junit4 being dropped in IntelliJ Gradle (though you can still just use junit4 without issuss) and now having issues with certain tests being ran, now would be a great time to migrate to Junit5.

From S.O

You can run junit4 tests with Junit5, we'll include the migration packages.

JUnit 5 provides a way out of the box

JUnit 5 = JUnit Platform + JUnit Jupiter + JUnit Vintage

Each one is a distinct project and using all of them allows to compile and execute JUnit 4 and JUnit 5 tests in a same project.

JUnit Jupiter is the combination of the new programming model and extension model for writing tests and extensions in JUnit 5.

JUnit Vintage provides a TestEngine for running JUnit 3 and JUnit 4 based tests on the platform

The JUnit Platform serves as a foundation for launching testing frameworks on the JVM

https://plugins.jetbrains.com/docs/intellij/testing-plugins.html#topics