Fix caluculation of m_resourcePath in the testing case

[daschuer]

It took me quite a while to figure that out. A related issue is that the path/line reported in the error message is wrong, because of a QML hack:

https://github.com/mixxxdj/mixxx/blob/main/src/controllers/scripting/legacy/controllerscriptenginelegacy.cpp#L763-L765

The hack allows statements like this:

import "." as Skin

instead of

import "../qml" as Skin

I would prefer to remove the hack and use the later, which feels correct for me.

[acolombier]

The reason for introducing this is to allow consistency with the QML code. As you can see with the S4 Mk3 PR, advanced mapping will likely consist of multiple QML file at different location, so I would rather allow some consistency on how you can import and reuse Mixxx component.

That being said, I agree that the current implementation is flawdd, and we should likely publish a QML module instead, which can be imported, along the lines of

import Mixxx.Skin 1.0 as Skin

[daschuer]

Filed a bug for the pass issue #14151

Ready for merge.