Possibility of merging (_)make_b2x from b_to_ddh_standalone.py into the (_)make_b2x that exists in b_builder.py

After !3035 (merged) is merged, it may be worth considering if we really need two separate (_)make_b2x in b_to_ddh_standalone.py and b_builder.py, as I noticed these look pretty much the same at first glance, other than a few different options added to one or the other.

This is absolutely not urgent to resolve, as if it were resolved it should have zero effect on rates. If I have time soon and find a proposed solution then I will create an MR and ask for it to be reviewed, and the MiCo can merge it at their convenience. There may be something I missed that makes the two (_)make_b2x incompatible, in which case I will leave things alone and close this issue.

The bonus also is that many lines that do not require make_b2ddh() of b_to_ddh_standalone.py can be moved from b_to_ddh_standalone.py to b_to_ddh.py