Merge topic 'install-export-xcframework'

37bc3400cd CMakePackageConfigHelpers: Add generate_apple_platform_selection_file()
256bb0cc40 install(EXPORT): Add ability to point to .xcframework file
a90968e044 cmExportBuildFileGenerator: Add structs for target exports

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Jason Juang <jasjuang@gmail.com>
Merge-request: !8969