[REQ] [Maven] Introduce addTestCompileSourceRoot

Created by: famod

Is your feature request related to a problem? Please describe.

I have to use build-helper-maven-plugin or fiddle around with maven-compiler-plugin when I am generating only for test execution (phase generate-test-sources) because there is only addCompileSourceRoot but no addTestCompileSourceRoot parameter.

Describe the solution you'd like

Introduce addTestCompileSourceRoot in analogy to addTestCompileSourceRoot.

Describe alternatives you've considered

build-helper-maven-plugin

Additional context

n/a