Introduce VirtualIdEmbeddable and IdClassEmbeddable

Added new form of `SqlExpressionResolver#createColumnReferenceKey`

Still need to
  - integrate EmbeddableInstantiator work
  - integrate embedded forms.  `VirtualIdEmbeddable` does not really need it as it can use the id-mapping itself as the embedded form.  But `IdClassEmbedded` should really be integrated
  - integrate `VirtualKeyEmbeddable` and `VirtualKeyEmbedded` for use as inverse composite fks
  - share `#finishInit` handling for `EmbeddableMappingType`, `VirtualIdEmbeddable` and `IdClassEmbeddable`

hibernate-core/src/main/java/org/hibernate/sql/ast/spi/SqlExpressionResolver.java

@@ -8,11 +8,14 @@
 
 import java.util.function.Function;
 
+import org.hibernate.metamodel.mapping.SelectableMapping;
 import org.hibernate.sql.ast.tree.expression.Expression;
 import org.hibernate.sql.ast.tree.from.TableReference;
 import org.hibernate.type.descriptor.java.JavaType;
 import org.hibernate.type.spi.TypeConfiguration;
 
+import static java.util.Locale.ROOT;
+
 /**
  * Resolution of a SqlSelection reference for a given SqlSelectable.  Some
  * SqlSelectable are required to be qualified (e.g. a Column) - this is indicated
@@ -54,6 +57,15 @@ static String createColumnReferenceKey(TableReference tableReference, String col
 		return qualifier + columnExpression;
 	}
 
+	/**
+	 * Convenience form for creating a key from TableReference and SelectableMapping
+	 */
+	static String createColumnReferenceKey(TableReference tableReference, SelectableMapping selectable) {
+		assert selectable.getContainingTableExpression().equals( tableReference.getTableExpression() )
+				: String.format( ROOT, "Expecting tables to match between TableReference (%s) and SelectableMapping (%s)", tableReference.getTableExpression(), selectable.getContainingTableExpression() );
+		return createColumnReferenceKey( tableReference, selectable.getSelectionExpression() );
+	}
+
 	/**
 	 * Given a qualifier + a qualifiable SqlExpressable, resolve the
 	 * (Sql)Expression reference.