Invalid syntax for Explicitly Implemented Interfaces (EII) in F#

[katebialiatka]

During a fix of #255, it was found that there is an inconsistency for EII in F#.

Currently, F# usage signature for EII interface is generated as: <MemberSignature Language="F#" Value="" Usage="CustomNamespace.CustomInterface.Prop1" /> However, F# article says that it should look like: let luckyLuke = (new Cowboy() :> ICowboy) luckyLuke.Draw()

Needs to investigate this deviation and fix the F# signature.

As an example to reproduce the issue, you can use a lib from integration tests. And here is an integration test to reproduce the issue.

Expected result - mdoc should generate syntax with the cast to the interface like in the example above.