qemu: command: Use JSON for QAPIfied -object directly

qemu: command: Use JSON for QAPIfied -object directly

Skip the lossy conversion to legacy commandline arguments by using the
JSON props directly when -object is QAPIfied. This avoids issues with
conversion of bitmaps and also allows validation of the generated JSON
against the QMP schema in the tests.

Since the new approach is triggered by a qemu capability the code
from 'virQEMUBuildObjectCommandlineFromJSON' in util/virqemu.c was moved
to 'qemuBuildObjectCommandlineFromJSON' in qemu/qemu_command.c which has
the virQEMUCaps type.

Some functions needed to be modified to propagate qemuCaps.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>