Align the regex implementation in SignificantTermsBuilder and TermsBuilder

[danielmitterdorfer]

In TermsBuilder we switched from java.util.Regex to org.apache.lucene.util.automaton.RegExp but SignificantTermsBuilder still uses java.util.Regex. We should align both implementations and use org.apache.lucene.util.automaton.RegExp consistently.

[colings86]

This should be done once the agg refactoring has been merged. Marking as stalled for now until that is complete

[ideadapt]

@colings86 & @danielmitterdorfer The aggregation refactoring has changed namings and structure of code. SignificantTermsAggregationBuilder uses org.apache.lucene.util.automaton.RegExp. I could not find any Terms related class that uses java.util.Regex.
Has this issue become obsolete?

[polyfractal]

It does indeed look like this issue is obsolete, I can't find any java.util.Regex either. Closing! :)