Merge Record and ExtensibleRecord types in the IR

Currently there are two separate constructors for Record and ExtensibleRecord in the IR: https://github.com/finos/morphir-elm/blob/55f27570f971e8c4e12fe1a0346dffdce594869e/src/Morphir/IR/Type.elm#L89-L90

These correspond to the following Elm code (excluding the left-hand-side):

type alias MyRecord =
    { foo : String
    }

type alias MyExtensibleRecord e =
    { e
        | foo : String
    }

The structure and semantics of the two definitions are very similar and in most cases the code that operates on them will share most of the logic so merging them will make the IR smaller and easier to process. This is one way to represent both with a single constructor:

    | Record a (Maybe Name) (List (Field a)) 

Acceptance Criteria

• The ExtensibleRecord constructor should be merged into the Record constructor as described above. https://github.com/finos/morphir-elm/blob/bc598079dd1d618ab6dfb5cb6116b215b323cfd7/src/Morphir/IR/Type.elm#L200-L201
• All usages across the codebase should be changed to use the new constructor.
• npm run build should complete successfully.
• elm-test should complete successfully.