Fix missing pythonic type hints for native_enum (#5619)

* fix missing pythonic type hints for native_enum

* Fix __qualname__ in native_enum

* Rename `enum class native` → `func_sig_rendering`. Add to `ENUM_TYPES_AND_MEMBERS`. Move new code around to fit in more organically.

"native" is used in so many places here, it would be very difficult to pin-point where the specific enum type is used.

Similarly, "value" is difficult to pin-point. Changed to "nested_value".

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Co-authored-by: Bryn Lloyd <12702862+dyollb@users.noreply.github.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rgrossekunst@nvidia.com>