Add `make_request<...>(...)` functions

[SSoelvsten]

Since the request<...> class has to be a POD, we should add make_request functions that

• make_request<...>(): Default initialise all values, e.g. the node carry with nil
• make_request<1, ...>(request<0>) Copy over all values and set the node carry to nil
• make_request<2, ...>(request<0>) Copy over all values and set the node carry to nil. Similarly for the argument having only one node carry.

And similarly make_request_data. Of course, they should be unit tested. Then, they can be used used in:

• bdd/if_then_else.cpp
• internal/algorithms/prod2.h
• internal/algorithms/quantify.h