[Enhancement] Optimize row-string converter

[scutzou]

What type of PR is this：

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Which issues of this PR fixes ：

Fixes #

Problem Summary(Required) ：

When inserting into RS table, we need to convert InternalRow to json or csv string. Previously this was implemented via AbstractRowStringConverter.fromRow. Even though the schema is definite, it still calls the convert method per row.

This PR has been tested on real data of 640 MB of orc data having almost 3 columns and 100 million rows, the Optimized stage with one partition is performed in 3 minutes compare to 9.1 minutes. Here below flame graphs for 120-sec sample of the execution of the test query using Spark 3.3 in local mode.

Before this PR:

spark ui

After this PR:

spark ui

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr will affect users' behaviors
• This pr needs user documentation (for new or modified features or behaviors)
• I have added documentation for my new feature or new function

[banmoy]

@scutzou Good optimization. Thanks very much