Inconsistencies in Path Handling

Path systems differ between QUL and QDS:

• QUL supports root QRC absolute paths.
• QDS supports only relative paths.

Needs urgent resolution. Suggested solution:

• Add QRC support to QDS.
• Allow certain folders to be assigned a QRC URL in the qmlproject file.
• Adjust lookup in qml2puppet (for both preview and puppet) using QAbstractFileEngineHandler.

Absolute QRC paths in MCU, with a few exceptions (see below), essentially map 1-to-1 to the paths relative to the project root, i.e. a QRC path qrc:/some/path corresponds to <project_root>/some/path for the majority of cases. This means that passing just the correct project root to qmlpuppet should suffice.

However that there's Project.projectRootPath property that changes the root of QUL project. Note that even if it is set, allegedly there must be a "default" project variant, normally corresponding to the actual project root.

Besides that in MCU there's ImageFiles.MCU.base property that effectively changes the "root" of the QRC resources. This is a MCU specific property, so supporting it in QDS is not trivial and most likely not needed, we can get by with just adding a warning in the Qt for MCUs documentation saying it is not supported in QDS.