Generated cmake configuration file is invalid with CMake 3.29.1

Summary

In the dune <module>-config.cmake files, we use the cmake variable PACKAGE_PREFIX_DIR for the initialization of the <module>_PREFIX variable. This PACKAGE_PREFIX_DIR seems to be only an internal variable and not mentioned in the cmake-documentation. With cmake 3.29 in MR https://gitlab.kitware.com/cmake/cmake/-/merge_requests/9390 the variable is renamed into something that we cannot directly use, PACKAGE_<MODULE>_COUNTER_<COUNTER> where the counter might be anything but is typically just 1.

So, we have to find a new way to determine the location for the <module>_PREFIX path. This must also be compatible between build and install environment.

Steps to reproduce

With cmake 3.29.1 configure dune-common, build, and install. The installed <install-prefix>/lib/cmake/dune-common/dune-common-config.cmake contains the empty variable set_and_check(dune-common_PREFIX "${PACKAGE_PREFIX_DIR}"). This is, because line 13 was changed

# from (cmake < 3.29.1)
get_filename_component(PACKAGE_PREFIX_DIR "${CMAKE_CURRENT_LIST_DIR}/../../../" ABSOLUTE)
# to (cmake = 3.29.1)
get_filename_component(PACKAGE_${CMAKE_FIND_PACKAGE_NAME}_COUNTER_1 "${CMAKE_CURRENT_LIST_DIR}/../../../" ABSOLUTE)

and thus the variable PACKAGE_PREFIX_DIR is now unset.

Reference

This issue was first reported in the Dune support chat by user Oromion.