[SPARK-14462][ML][MLLIB] add the mllib-local build to maven pom

## What changes were proposed in this pull request?

In order to separate the linear algebra, and vector matrix classes into a standalone jar, we need to setup the build first. This PR will create a new jar called mllib-local with minimal dependencies. The test scope will still depend on spark-core and spark-core-test in order to use the common utilities, but the runtime will avoid any platform dependency. Couple platform independent classes will be moved to this package to demonstrate how this work.

## How was this patch tested?

Unit tests

Author: DB Tsai <dbt@netflix.com>

Closes #12241 from dbtsai/dbtsai-mllib-local-build.