The resteasy reactive param converter, which gets automatically generated, calls the fromString/valueOf/constructor of the wrapper class directly. This fails if the paramconveter and the wrapper class is housed in different class loader. We can ensure that the TCCL is the same CL as the wrapper class, by not considering the wrapper an application class anymore if it is in an external jar.

related to #47471

This reverts #39691 (but also adds tests)
Follows up on #39823