Allow to specify `named-values` **in addition** to `allowed-values` for `enum` types

[Vampire]

Currently we only generate constant values for enums from their content.
If you have quite long or awkward possible values like the terms of use URL of the setup-gradle action, the names are a bit unhandy.

Additionally, if you have an enum with values that calculate to the same name like

inputs:
  some-enum:
    type: enum
    allowed-values:
      - foo-bar
      - foo_bar

which both evaluate to FooBar, you get a 500 internal server error as soon as you request the JAR, because a compile error will happen when trying to compile the bindings.

The latter could maybe also be solved by some logic to make the names unique,
but it could also be solved by this feature request which means, that you can give explicit names for enum values.

I think it makes sense to allow unnamed and named in the same element.

[krzema12]

Makes sense!

Impl-wise, I'm thinking about adding allowed-named-values where we'd have a dictionary of:

NamedValue1: Value1
NamedValue2: Value2
...

and it would be mutually exclusive with allowed-values. WDYT?

[Vampire]

Would also be a way, but then you have to specify all names explicitly which might be tedious like

named-values:
  Foo: foo
  Bar: bar
  Baz: baz
  Boo: boo
  ShortOne: really-long-one-that-you-want-to-shorten-for-the-user

while my original idea was more just to be able to provide an alias for some like

allowed-values:
  - foo
  - bar
  - baz
  - boo
  - really-long-one-that-you-want-to-shorten-for-the-user
named-values:
  ShortOne: really-long-one-that-you-want-to-shorten-for-the-user

or maybe

allowed-values:
  - foo
  - bar
  - baz
  - boo
named-values:
  ShortOne: really-long-one-that-you-want-to-shorten-for-the-user

No sure whether it should really be a new keyword, I would see it semantically identical to the other named-values. 🤷‍♂️

[krzema12]

Would also be a way, but then you have to specify all names explicitly which might be tedious

I actually thought about specifying only the ones that we want to have a name for, and for the remaining values, we'd use the default rules of building an enum entry from a value.

However, now I actually like the idea of reusing named-values for it. From the two options you showed, I'd go with explicitly listing all allowed values under allowed-values, not just not named ones.