IllegalArgumentException in QueryParserBase.parse() [LUCENE-6703]

I have encountered a very special case where parsing a certain String with the `MultiFieldQueryParser` causes an `IllegalArgumentException` thrown in the constructor of `org.apache.lucene.util.automaton.RegExp`. I would have expected a `ParseException` instead (as stated in the API doc).

```Java
QueryParser parser = new MultiFieldQueryParser(...);
parser.parse("/x)/");
```

The "evil" search string is **`/x)/`**.

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Migrated from [LUCENE-6703](https://issues.apache.org/jira/browse/LUCENE-6703) by Oliver Becker

Start by reproducing the issue with MultiFieldQueryParser.parse("/x)/") and trace where the IllegalArgumentException from org.apache.lucene.util.automaton.RegExp escapes the parser. Compare this behavior with the API's ParseException contract; done means the malformed query produces the documented exception instead.

Written by the indexing model from the issue text.