Large integers previously got capped to LLONG_MAX/LLONG_MIN so we could
store them as int64_t. This could lead to silent errors occuring.

Now, we use a double to handle these cases.

Add a test to confirm that QMPInputVisitor handles this as expected if
we're expected an integer value: errors for out of range integer values
that got promoted to doubles in this fashion.
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>
Reviewed-by: NLaszlo Ersek <lersek@redhat.com>
Reviewed-by: NAmos Kong <akong@redhat.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>