[SPARK-3063][SQL] ExistingRdd should convert Map to catalyst Map.

Currently `ExistingRdd.convertToCatalyst` doesn't convert `Map` value.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1963 from ueshin/issues/SPARK-3063 and squashes the following commits:

3ba41f2 [Takuya UESHIN] Merge branch 'master' into issues/SPARK-3063
4d7bae2 [Takuya UESHIN] Merge branch 'master' into issues/SPARK-3063
9321379 [Takuya UESHIN] Merge branch 'master' into issues/SPARK-3063
d8a900a [Takuya UESHIN] Make ExistingRdd.convertToCatalyst be able to convert Map value.
[SPARK-3226][MLLIB] doc update for native libraries

to mention `-Pnetlib-lgpl` option. atalwalkar

Author: Xiangrui Meng <meng@databricks.com>

Closes #2128 from mengxr/mllib-native and squashes the following commits:

4cbba57 [Xiangrui Meng] update mllib dependencies
[SPARK-2839][MLlib] Stats Toolkit documentation updated

Documentation updated for the Statistics Toolkit of MLlib. mengxr atalwalkar

https://issues.apache.org/jira/browse/SPARK-2839

P.S. Accidentally closed #2123. New commits didn't show up after I reopened the PR. I've opened this instead and closed the old one.

Author: Burak <brkyvz@gmail.com>

Closes #2130 from brkyvz/StatsLib-Docs and squashes the following commits:

a54a855 [Burak] [SPARK-2839][MLlib] Addressed comments
bfc6896 [Burak] [SPARK-2839][MLlib] Added a more specific link to colStats() for pyspark
213fe3f [Burak] [SPARK-2839][MLlib] Modifications made according to review
fec4d9d [Burak] [SPARK-2830][MLlib] Stats Toolkit documentation updated