Backport fix in StandardHippoAnalyzer discovered by Sonar, REPO-722

For performance reasons, it is good and not risky to backport the fix in StandardHippoAnalyzer to 7.8. The tokenStream methods was creating a new HashMap from the stop words array every time it was invoked, and the static default stop words array was overwritten every time an analyzer was instantiated, instead of being initialized once in a static block.