Do not store union case compiled name

[auduchinok]

It seems storing the name is needed only as a workaround for opNameCons and opNameNil cases and can be computed from Id then same way when needed instead.

[alfonsogarciacaro]

Is the CompiledNameAttribute actually used in union cases? We use it in multiple occasions in Fable, but there doesn't seem to be a way to get it through reflection in .NET and we need to check the attribute manually.

[auduchinok]

@alfonsogarciacaro No, they're ignored, at least currently.
Details of compiled forms and names of union cases are described in 8.5.4 of the F# 4.1 spec.
13.1 chapter also tells where attributes are placed for union cases in compiled form, making CompiledName case look a bit weird, although funny:

type U =
    | [<CompiledName("AA")>] A of int

[CompiledName("AA")]
[CompilationMapping]
public static Module.U NewA(int item)
{
  return new Module.U(item);
}

The spec says following for the attribute itself:

Changes the compiled name of an F# language construct. This attribute should be used only in F# assemblies.

So it could override names coming from 8.5.4, but I'm not sure it's ever going to change.

[auduchinok]

It's ready. I've changed error ranges for the following error to only contain case names and not full case ranges:

The union case named 'Tags' conflicts with the generated type 'Tags'