[SPARK-14906][ML] Copy linalg in PySpark to new ML package

## What changes were proposed in this pull request?

Copy the linalg (Vector/Matrix and VectorUDT/MatrixUDT) in PySpark to new ML package.

## How was this patch tested?
Existing tests.

Author: Xiangrui Meng <meng@databricks.com>
Author: Liang-Chi Hsieh <simonh@tw.ibm.com>
Author: Liang-Chi Hsieh <viirya@gmail.com>

Closes #13099 from viirya/move-pyspark-vector-matrix-udt4.

python/docs/pyspark.ml.rst

@@ -41,6 +41,14 @@ pyspark.ml.clustering module
     :undoc-members:
     :inherited-members:
 
+pyspark.ml.linalg module
+----------------------------
+
+.. automodule:: pyspark.ml.linalg
+    :members:
+    :undoc-members:
+    :inherited-members:
+
 pyspark.ml.recommendation module
 --------------------------------