[Development] Using qml.exe with a custom QML_ELEMENT plugin

[Ulf Hermann]

> PS C:\Qt\6.7.0\msvc2019_64\bin> /.\qml.exe -I 
> "C:\Code\Cpp\build-qml-plugin-minimal-Desktop_Qt_6_7_0_MSVC2019_64bit-Release" -f "C:\Code\Cpp\qml-plugin-minimal\Main.qml"
> QQmlApplicationEngine failed to load component
> file:///C:/Code/Cpp/qml-plugin-minimal/Main.qml:5:1: Die Bibliothek 
> C:\Code\Cpp\build-qml-plugin-minimal-Desktop_Qt_6_7_0_MSVC2019_64bit-Release\Hello\World\Worldplugin.dll kann nicht geladen werden: Das angegebene Modul wurde nicht gefunden.
> qml: Did not load any objects, exiting./

On windows, you have to jump through some hoops to make it find the 
backing library. There is PATH. You can install the backing library in 
some place that's already on your PATH or you can adapt PATH. If you 
have a custom executable you can also install the backing library next 
to it.