qtbase(qt6): Enforce no x11-native gets pulled in and fix issues in qt6 layer, fix...

qtbase(qt6): Enforce no x11-native gets pulled in and fix issues in qt6 layer, fix llvm vs. clang

Workaround: Fix wrong detection of X11 headers in native sysroot.
For now remove xkbcommon

Limit qt6 packagegroup inclusion to avoid unnecessary content in image.

Also remove old patch to qtmultimedia.

meta-clang inclusion now needs
https://github.com/kraj/meta-clang/tree/scarthgap?tab=readme-ov-file#providing-llvm

thus add

PREFERRED_PROVIDER_llvm = "clang"
PREFERRED_PROVIDER_llvm-native = "clang-native"
PREFERRED_PROVIDER_nativesdk-llvm = "nativesdk-clang"
PROVIDES:pn-clang = "llvm"
PROVIDES:pn-clang-native = "llvm-native"
PROVIDES:pn-nativesdk-clang = "nativesdk-llvm"

Need to work out the final location for these.

Bug-AGL: SPEC-5282

Change-Id: Ib3ed9e81ecd1e27681e443dacddac5fec42a303f
Signed-off-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/30503