Move tests next to the files they are testing in Angular

[kaidohallik]

As per #13125 (comment) this PR moves tests next to the files they are testing.

This PR has 2 commits:

• first moves tests next to the files they are testing
• second polishes imports in tests, using ./ for files which are next to test

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• All continuous integration tests are green
• Tests are added where necessary
• jhipster-online was updated if necessary
• Documentation is added/updated where necessary
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[DanielFran]

@kaidohallik Trusting you on this. Feel free to merge if you are confident
Just restarted 1 flaky test...

[DanielFran]

LGTM

[mshima]

The only problem I see it that we are removing the entire spec folder.
So if there are custom files there, they will be removed.
Not sure how to proceed here, but I think it's important to keep this in mind.

Solutions:

• Remove file by file.
• Make jhipster upgrade the only supported upgrade path for this use case.

[kaidohallik]

I thought that they can revert their own files deletions. But you are right @mshima it's better to do clean up file by file. So I'm doing additional PR for cleaning test files file by file.