Support for `qmlls` and `qmllint`

[LeonMatthesKDAB]

As we're reworking the build system for QML modules anyhow, we should make sure to add support for qmlls and qmllint if possible.

See also: #974 and #657

[dlon]

Is there a workaround for qmlls? We still see some missing imports using a manually generated .qmlls.ini and are not sure where to find them:

::rust::cxxqt1::CxxQtThreading<MullvadApp> was not found. Did you add all imports and dependencies? [import]

Here's .qmlls.ini:

[General]
buildDir=<repo here>/target/debug/build/mullvadvpn-4265a9dd3bcb2d38/out/qt-build-utils/qml_modules
no-cmake-calls=true
importPaths=/usr/lib64/qt6/qml

[LeonMatthesKDAB]

Unfortunately not at the moment.
I have tried to resolve the remaining issues with qmllls, but even if this initial issue is resolved, most property types will not be recognized by qmlls, as it doesn't understand what e.g. std::unit32_t is, which is the Rust-compatible type CXX-Qt uses.
This will require more work and possibly support from qmlls itself.