Constify all opaque Property pointers

Constify all opaque Property pointers

Via sed "s/  Property [*]/  const Property */".

The opaque pointers passed to ObjectProperty callbacks are
the last instances of non-const Property pointers in the tree.
For the most part, these callbacks only use object_field_prop_ptr,
which now takes a const pointer itself.

This logically should have accompanied d36f165d952 which
allowed const Property to be registered.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Lei Yang <leiyang@redhat.com>
Link: https://lore.kernel.org/r/20241218134251.4724-25-richard.henderson@linaro.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>