[non-BE] Implements first version of proper EXT out for MASA in JBM operation.

Related to #470 (closed).

This implements the required EXT out for MASA in JBM operation. The solution is not ideal in our opinion but it is what could be completed in this time frame. The provide approach uses even distribution of time-modified slots in the output subframes. The metadata mapping for MASA rendering is also affected to be unified with the EXT out version, thus not creating unnecessary output differences between internal and external renderers.