Qt6 Wayland CMake Configs reference uninstalled files for Private Includes

[cola]

When trying to build Qt6 based kwayland against qt6-wayland, I noticed that

usr/include/${DEB_HOST_MULTIARCH}/qt6/QtWaylandClient/6.*
usr/include/${DEB_HOST_MULTIARCH}/qt6/QtWaylandCompositor/6.*
usr/include/${DEB_HOST_MULTIARCH}/qt6/QtWaylandEglClientHwIntegration/6.*
usr/include/${DEB_HOST_MULTIARCH}/qt6/QtWaylandEglCompositorHwIntegration/6.*
usr/include/${DEB_HOST_MULTIARCH}/qt6/QtWaylandGlobal/6.*
usr/include/${DEB_HOST_MULTIARCH}/qt6/QtWlShellIntegration/6.*

which are currently in not-installed, need to be installed, because of file locations are referenced by CMake.

Here the debug output of the kwayland build:

CMake Error in src/client/CMakeLists.txt:
  Imported target "Qt6::WaylandClientPrivate" includes non-existent path

    "/usr/include/x86_64-linux-gnu/qt6/QtWaylandGlobal/6.4.2"

  in its INTERFACE_INCLUDE_DIRECTORIES. Possible reasons include:

  * The path was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and references files it does not
  provide.

CMake Error in src/client/CMakeLists.txt:
  Imported target "Qt6::WaylandClientPrivate" includes non-existent path

    "/usr/include/x86_64-linux-gnu/qt6/QtWaylandGlobal/6.4.2"

  in its INTERFACE_INCLUDE_DIRECTORIES. Possible reasons include:

  * The path was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and references files it does not
  provide.

CMake Error in src/client/CMakeLists.txt:
  Imported target "Qt6::WaylandClientPrivate" includes non-existent path

    "/usr/include/x86_64-linux-gnu/qt6/QtWaylandGlobal/6.4.2"

  in its INTERFACE_INCLUDE_DIRECTORIES. Possible reasons include:

  * The path was deleted, renamed, or moved to another location.

  * An install or uninstall procedure did not complete successfully.

  * The installation package was faulty and references files it does not
  provide.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Tanmoy Saha (t4saha)]

The Ubuntu repository is missing the -private-dev or -private packages for Qt6-wayland.