Incorrect propagation of iOS bitcode and -fapplication-extension flags to user projects

The build system currently adds bitcode compile and link flags on the PlatformCommonInternal target, with the intention that the flags are only added when building Qt itself, so Qt modules, plugins, etc.

For user projects, it's up to the Xcode setting of ENABLE_BITCODE whether user project code should build with bitcode or not.

Currently the internal flags spill out and get forcefully added to user projects, effectively forcing bitcode to always be on for user projects.

The same happens with the -fapplication-extension flags is static build of iOS and macOS.