Dp container copy

[bocchino]

Fixes to DP container copying, as discussed. Note that a small change to FPP code gen is required. For now I have hand-coded the workarounds and marked them with TODOs.

[bocchino]

@LeStarch FYI.

[timcanham]

So the DpContainer::copyMembersFrom() is a temporary measure until there is new FPP?

[bocchino]

When there's new FPP code gen, these lines will go away:

https://github.com/bocchino/fprime/blob/43885911748eb6369e66809064bde6ac61da5c71/Ref/SignalGen/SignalGen.cpp#L283-L284

[bocchino]

I'm proposing to keep the copyMembersFrom syntax. As discussed, it's more explicit about what's going on than an overloaded operator=.

[timcanham]

I thought that was just for the underlying ExternalSerializeBuffer. I think the container should have an = operator.

[bocchino]

OK, when I update the FPP code gen I can add a protected operator= in the base class and add a public operator= in the derived class that calls it. I don't want to add a public operator= in the base class -- that's contrary to C++ coding rules.

[bocchino]

Closing in favor of #20.