[SPARK-16372][MLLIB] Retag RDD to tallSkinnyQR of RowMatrix

## What changes were proposed in this pull request?

The following Java code because of type erasing:

```Java
JavaRDD<Vector> rows = jsc.parallelize(...);
RowMatrix mat = new RowMatrix(rows.rdd());
QRDecomposition<RowMatrix, Matrix> result = mat.tallSkinnyQR(true);
```

We should use retag to restore the type to prevent the following exception:

```Java
java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Lorg.apache.spark.mllib.linalg.Vector;
```

## How was this patch tested?

Java unit test

Author: Xusen Yin <yinxusen@gmail.com>

Closes #14051 from yinxusen/SPARK-16372.