ReflectionClass: show enums differently from classes, test output

[DanielEScherzer]

While internally enums are mostly the same as classes, their output in
ReflectionClass::__toString() should show the enum as the developer wrote it,
rather than as the engine stored it. Accordingly

• Say that the enum is an enum, not a final class

• Include the backing type, if any, in the declaration line

• Remove the UnitEnum and BackedEnum interfaces from the list of interfaces
  implemented

• List enum cases separately from constants, and show the underlying values, if
  any

Also add tests for the output - the tests are added in the first commit, so
that the changes in the second commit can be more easily confirmed.

GH-15766

[nielsdos]

I didn't look at the code, but in general I'm in favor of the idea. It's too late for 8.4 though, and this may have BC implications if people rely on the output. So when we start on 8.5 you may need to email the ML to pitch this.

[DanielEScherzer]

I didn't look at the code, but in general I'm in favor of the idea. It's too late for 8.4 though, and this may have BC implications if people rely on the output. So when we start on 8.5 you may need to email the ML to pitch this.

Yeah, there is no rush on this. Just wondering though, is the next version going to be 8.5, or 9.0? I wasn't able to find documentation on how many minor releases are done for each major release - since the github milestones show 8.4 and then 9.0, I assumed 9.0 was next - whichever it is, this can totally wait

[nielsdos]

The version will be bumped to 9.0 if it's necessary to do so (e.g. large engine changes).
The next version is most likely 8.5 unless decided otherwise.