Bug: Roundtrip issue: relational class mapping `primaryKey` field is not handled properly during transformation

[akphi]

🐛 Bug Report

Relational class mapping primaryKey is added after transformation metamodel -> protocol

How to reproduce the issue

Use the following grammar in manual grammar roundtrip test - See https://github.com/finos/legend-studio/issues/165 for more details

Class other::Person
{
    name:String[1];
    firm:other::Firm[1];
    address: other::Address[0..1];
}
Class other::Firm
{
    legalName:String[1];
    employees:other::Person[1];
    address:other::Address[1];
}
Class other::Address
{
    line1:String[1];
}
###Relational
Database mapping::db(
   Table employeeFirmDenormTable
   (
    id INT PRIMARY KEY,
    name VARCHAR(200),
    firmId INT,
    legalName VARCHAR(200),
    address VARCHAR(200)
   )
)
###Mapping
Mapping mappingPackage::myMapping
(
    other::Person: Relational
    {
        name : [mapping::db]employeeFirmDenormTable.name,
        firm
        (
            ~primaryKey ([mapping::db]employeeFirmDenormTable.legalName)
            legalName : [mapping::db]employeeFirmDenormTable.legalName,
            address
            (
                line1: [mapping::db]employeeFirmDenormTable.address
            )
        ),
        address
        (
            line1: [mapping::db]employeeFirmDenormTable.address
        )
    }
)

Solution idea

We should properly create an InferableValue wrapper around this or do some logic in the transformer to omit primaryKey when it's not needed.