HHH-17002, HHH-18820, HHH-19391, HHH-18514 fix generated aliases

Oracle disapproves of aliases of form "_1"

Author: gavinking

hibernate-core/src/main/java/org/hibernate/query/sqm/tree/AbstractSqmStatement.java

@@ -103,6 +103,6 @@ public Set<ParameterExpression<?>> getParameters() {
 
 	@Override
 	public String generateAlias() {
-		return "_" + (++aliasCounter);
+		return "t_" + (++aliasCounter);
 	}
 }

hibernate-core/src/main/java/org/hibernate/query/sqm/tree/select/SqmSelectStatement.java

@@ -596,6 +596,6 @@ else if ( !newSelections.contains( selection ) ) {
 
 	@Override
 	public String generateAlias() {
-		return "_" + (++aliasCounter);
+		return "t_" + (++aliasCounter);
 	}
 }