Provide a way of optionally importing or selecting modules

QtQuick.Controls selects a style to be imported at runtime by evaluating a file qtquickcontrols2.conf and some environment variables. Additionally it allows the style to be selected via C++.

We want something similar for QtQml.WorkerScript. Usage of WorkerScripts is not very common and forcing everyone to load the workerscript plugin is a waste. There should be a way of declaring an import as optional in a qmldir file:

optional import QtQml.WorkerScript auto

This would import WorkerScript if the user has not specified otherwise. However, a per-application configuration file or an environment variable might customize the behavior. This would supersede the current qtquickcontrols2.conf, and make the behavior configured in there accessible to QML tooling.

[QtQml]
Import=QtQml.Models,MyOwnStaticImport
OtherThings=Foo,Bar

[QtQuick.Controls]
Import=QtQuick.Controls.Material

[QtQuick.Controls.Material]
Theme=Light
Accent=Teal
Primary=BlueGrey

The file would be read by the QML engine and the Import configurations would be applied when loading a module. Other entries would be made available through public API.