Previously, the headers are installed as ${CMAKE_INSTALL_PREFIX}/include/cmake_package_name, where cmake_package_name is the CMake package name, e.g., PySide6. In the wheels, the headers were included as package_name/include. Since the level of the include directory is different, this caused issues when importing the CMake package in a downstream project. - This change modifies the installation of the headers so that the CMake install prefix and the wheels are consistent. - Additionally - this change adds the libpyside6 headers to the wheels. - The include headers for libshiboken were shipped with shiboken6-generator and not with shiboken6, which has the libshiboken binary. Change-Id: I96e3280799da169836e24551b906274f5b0fc962 Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>