[SPARK-17456][CORE] Utility for parsing Spark versions

## What changes were proposed in this pull request?

This patch adds methods for extracting major and minor versions as Int types in Scala from a Spark version string.

Motivation: There are many hacks within Spark's codebase to identify and compare Spark versions. We should add a simple utility to standardize these code paths, especially since there have been mistakes made in the past. This will let us add unit tests as well.  Currently, I want this functionality to check Spark versions to provide backwards compatibility for ML model persistence.

## How was this patch tested?

Unit tests

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #15017 from jkbradley/version-parsing.