xcf : use check for visionos build version (#3021)

xcf : use check for visionos build version (#3021)

This commit adds a check for the visionos build version used with vtool
in build-xcframework.sh. The script now checks the Xcode version and
determines whether to use "xros" or "visionos" for the build version.

This commit also uses xcrun for the vtool so that the version of vtool
in xcode command line tools is used instead of the one in the system
path.

Refs: https://github.com/ggml-org/whisper.cpp/pull/2994#issuecomment-2773292223