[I-Build-Tests] Inline 'testAll' scripts

[HannesWell]

This is currently a draft since I have to test this locally first.

As a follow-up we could consider to inline the runtests.sh/bat scripts as well or at least to simplify them to what's still relevant nowadays.
Keeping might be interesting for those that run I-builds locally, but on the long run I would like to simplify the set up to an extend so that we can provide a simple launch config to run the I-build locally for the current platform and with the current config in this repo. The compiled archives would then be either provided locally (if one wants to test changes) or be fetched from a matching I-build. But that's another story.

[akurtakov]

@HannesWell Do you plan any other work here? If not I would like to merge this one.

[HannesWell]

I don't plan more work a.t.m. but I have to check first that this will really work as expected.
Plan to do it in the next days.
And if there remains some uncertainty I prefer to submit it Friday evening so that I can easily fix this at the weekend without disturbing too much.