Clean up Git submodules and ruling tests

[victor-diez-sonarsource]

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[ilia-kebets-sonarsource]

I'll give my review here as the diff is too large to work on github:

1. I don't know if it's a local duplicate, but there's a its/ruling/src/test/expected/jsts/jsts folder holding a copy of the JS projects
2. document why we do cleanRootNodeModules()
3. put javascript-test-sources/ projects at root level like the others

[ilia-kebets-sonarsource]

LGTM.
As discussed, what is left to do for this task is:

1. communicate instructions to the squad on how to update to this new folder layout
2. write to REs to change the name of the sources repo
3. apply this update in the code

[sonarqube-next]

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