Generating a Kotlin project with a package name containing keywords will result in an unusable project

[Ant00000ny]

fix #1550

Initializer does not escape package names containing kotlin keywords, and generates unusable project. This fix checks for hard keywords (from offcial doc, Kotlin does not provide method like javax.lang.model.SourceVersion#isKeyword in Java)

[mhalbritter]

Hey, thanks for the PR. I think there's something missing: i just tested with the package name package.class.fun.example and expected package, class and fun to be escaped. However, the resulting package name is com.example.demo and there's this note in the readme:

* The original package name 'package.class.fun.example' is invalid and this project uses 'com.example.demo' instead.

I think the code in io.spring.initializr.metadata.InitializrConfiguration#hasReservedKeyword is interfering with that. It still works under the assumption that the Java keywords apply to every other language.

[Ant00000ny]

Thank you. I'm not sure if it is ok to just add a parameter isKotlin to io.spring.initializr.metadata.InitializrConfiguration#cleanPackageName amd skip Java keyword checks for Kotlin in this method?

[mhalbritter]

Thank you very much and congratulations on your first contribution 🎉!

I've polished the changes a bit in bce08cf.