temporarily reintegrate libformfactor in BornAgain

To facilitate forthcoming API changes.

Once the API is stable, we need to

• overwrite libformfactor/ff with BornAgain/ff
• remove BornAgain/ff
• remove add_subdirectory(ff) from BornAgain/CMakeLists.txt
• uncomment find_package(formfactor REQUIRED) in BornAgain/cmake/BornAgain/Dependences.cmake

added CMake label

changed the description

enabled an automatic merge when the pipeline for 387ddfac succeeds

aborted the automatic merge because source branch was updated

added 1 commit

• fcc6580e - CMake corr: no need to include formfactor above Base

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added 1 commit

• a2942d86 - corr (formfactor0 -> formfactor; linked only to Sample)

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changed the description

merged

mentioned in commit f4538e12