## What changes were proposed in this pull request?

StringIndexerModel.transform sets the output column metadata to use name inputCol.  It should not.  Fixing this causes a problem with the metadata produced by RFormula.

Fix in RFormula: I added the StringIndexer columns to prefixesToRewrite, and I modified VectorAttributeRewriter to find and replace all "prefixes" since attributes collect multiple prefixes from StringIndexer + Interaction.

Note that "prefixes" is no longer accurate since internal strings may be replaced.

## How was this patch tested?

Unit test which failed before this fix.

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

Closes #11965 from jkbradley/StringIndexer-fix.