message: Make Schema._schemaKey protected for imse-core
diff: @@ -24,7 +24,7 @@ const SCHEMAURL3_1 = "https://dev.bentley.com/json_schemas/ec/31/draft-01/ecsche
  */
  export default class Schema implements CustomAttributeContainerProps {
  private _context?: SchemaContext;
  - private _schemaKey?: SchemaKey;
  + protected _schemaKey?: SchemaKey;
  public alias: string;
  public label?: string;
  public description?: string;
  