Improve Gradle idea task so it generates isolated main/test classpaths per module

The IntelliJ control files generated by the Gradle IDEA plugin wrongly share the `testRuntime` classpath of `servicetalk-http-router-jersey` with `servicetalk-data-jackson-jersey`, which unfortunately gives access to `jersey-media-json-jackson`. This makes many tests in `servicetalk-data-jackson-jersey` fail because they are built specifically for ST's Jackson serializer. Thus we disable the test suite altogether if we're in this scenario to prevent overwhelming developers with meaningless and puzzling failures [1].

It would be much better to improve the `idea` task to generate isolated main/test classpaths per module, the same way the IDEA Gradle plugin does.

[1] https://github.com/servicetalk/servicetalk/blob/master/servicetalk-data-jackson-jersey/src/test/java/io/servicetalk/data/jackson/jersey/JerseyDataJacksonTestSuite.java#L48-L52

Start with the Gradle `idea` task and compare its generated control files with the behavior of the IDEA Gradle plugin. Use `servicetalk-data-jackson-jersey/src/test/java/io/servicetalk/data/jackson/jersey/JerseyDataJacksonTestSuite.java` to reproduce the classpath contamination. Done means each module has isolated main and test classpaths and the affected tests no longer see unrelated Jersey dependencies.

Written by the indexing model from the issue text.