This change does a few things:
* Improves compile times because the gen.cpp is inlined so less header parsing is required.
* Allows us to forward declare more types in the headers where we were not able to because the gen.cpp files did not have all the required headers included. The gen.cpp files required the header that generated it to include all the types because of the constructor and desructor in the gen.cpp need to know the full type.
#jira
#preflight 6323b43f8131e92d65aed1d9
[CL 22064061 by bryan sefcik in ue5-main branch]
e5edfdd06d