PARQUET-1740: Make ParquetFileReader.getFilteredRecordCount public

[wangyum]

Make sure you have checked all steps below.

Jira

https://issues.apache.org/jira/browse/PARQUET-1740

Tests

• My PR adds the following unit tests OR does not need testing for this extremely good reason:

Commits

• My commits all reference Jira issues in their subject lines. In addition, my commits follow the guidelines from "How to write a good git commit message":
  1. Subject is separated from body by a blank line
  2. Subject is limited to 50 characters (not including Jira issue reference)
  3. Subject does not end with a period
  4. Subject uses the imperative mood ("add", not "adding")
  5. Body wraps at 72 characters
  6. Body explains "what" and "why", not "how"

Documentation

• In case of new functionality, my PR adds documentation that describes how to use it.
  • All the public functions and the classes in the PR contain Javadoc that explain what it does

[gszadovszky]

The failure is not related to this change. See PARQUET-1741 for details.
I'll restart the checks after the issue is fixed.

[Fokko]

@wangyum Can you rebase?