fix(overlay): properly handle horizontal positioning in rtl directionality

Author: josephperrott

src/cdk/overlay/position/global-position-strategy.ts

@@ -178,6 +178,8 @@ export class GlobalPositionStrategy implements PositionStrategy {
         parentStyles.justifyContent = 'flex-end';
       } else if (this._justifyContent === 'flex-end') {
         parentStyles.justifyContent = 'flex-start';
+      } else {
+        parentStyles.justifyContent = this._justifyContent;
       }
     } else {
       parentStyles.justifyContent = this._justifyContent;