Currently we hard-code to look for qml plugin Config.cmake files
in the current list dir, whether the Qt6Qml directory is.
This is not sufficient for finding qml plugins in a prefix build of a
repo that has not been installed yet.
For example qtquick3d plugins will be in
qtquick3d_build_dir/lib/cmake/Qt6Qml/QmlPlugins, which
won't be picked up by the Qt6Qml Config file in the installed Qt
location.
Allow specifying extra qml plugin glob prefixes via a new
QT_ADDITIONAL_QML_PLUGIN_GLOB_PREFIXES variable.
This is similar to QT_ADDITIONAL_PACKAGES_PREFIX_PATH.
Any path specified via QT_ADDITIONAL_QML_PLUGIN_GLOB_PREFIXES
will have the
QmlPlugins/${INSTALL_CMAKE_NAMESPACE}*Config.cmake
glob appended to it, and then used for globbing files in that
location, after processing the main location wherever Qt6Qml is.
This will be used by ExternalProject example machinery.
Task-number: QTBUG-90820
Task-number: QTBUG-96232
Change-Id: I469863c965b8b13cf007c611976a64fbff6e9111
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
40fa36db22