See note in comment; concrete example of build error (when building
syncthingtray against qtforkawesome built with CMake 3.24.0):
```
CMake Error at plasmoid/lib/CMakeLists.txt:15 (find_package):
Found package configuration file:
/usr/share/qtquickforkawesome-git/cmake/qtquickforkawesome-gitConfig.cmake
but it set qtquickforkawesome-git_FOUND to FALSE so package
"qtquickforkawesome-git" is considered to be NOT FOUND. Reason given by
package:
The following imported targets are referenced, but are missing:
qtforkawesome-git
```
Some backend libraries of Syncthing Tray and Reflective RapidJSON only use
certain headers of qtutilities/c++utilities. The current solution did not
really work because it did not distinguish between the build and install
interface and also did not take compile definitions and options into
account.
* Also enable the "lib" prefix which CMake would add by default again; it
has only been removed to preserve compatibility with qmake when switching
from qmake to CMake
* None of these changes are enabled by default to preserve compatibility
Use-case is explained in the documentation. This implementation
takes care that the additional libs actually occur at the end
of the linker line despite the use of imported targets with
INTERFACE_LINK_LIBRARIES. It might still not be perfect but
sufficient for current use-cases.
* Prevent imported library paths pointing to build directory
ending up in pkg-config file
* Handle targets which reference other targets but have not pkg-config
module
* Fix check for BUNDLED_TARGETS
Even if QMake tells us that would be the right location because
it breaks development setups which use a custom install prefix
and set QT_PLUGIN_PATH accordingly.
* Allow exporting targets from 3rd party projects which are
built within my own projects. This is required if the build
scripts of these 3rd party projects don't have an export on
their own but are used in the public interface or as a dependency
of a static library.
* Add those libraries to the pkg-config file as well.