Add the generatedSourcesPath to the project source roots again

[mensinda]

Followup for #191 to add back the generatedSourcesPath to the maven project paths.

This seems to work, but the solution feels a bit hacky.

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[mensinda]

I have converted this PR to a draft, since I made an alternative implementation in #312, which is cleaner IMHO.

[slawekjaranowski]

@mensinda as #312 was merged I suppose that this can be closed

[mensinda]

Yes, with #312 merged, this is no longer needed.