LUCENE-7064: Make MultiPhraseQuery immutable

[LucVL]

This PR is based at the highest commit point common to master, branch_6x and branch_6_0 so it should be easy to merge with any or all of them.

My original mail to the dev list doesn't seem to get through, so I repeat it here:

While checking how to migrate my custom components from lucene/solr 5.1 to 6.x I stumbled upon the fact that oal.search.MultiPhraseQuery is not immutable like most other implementations (see e.g.: https://issues.apache.org/jira/browse/LUCENE-6531)

Since it is part of the public API I would suggest splitting it in an immutable class and a builder like was done for most other Queries before releasing an official 6.x version.

I did a quick scan through all derived classes of Query and I compiled the following list (ignoring sources in test or contrib folders)
Some of them are already marked as experimental (but should perhaps receive the "official" @lucene.experimental tag ?)
For some it's possibly not an issue since they should never end up in a filter cache (like MoreLikeThisQuery ?), but then a comment specifying the exception to the rule should perhaps be added.

I'll probably already have a go at the MultiPhraseQuery case shortly and create a JIRA issue with a PR for it.

Luc Vanlerberghe

lucene/search:

• org.apache.lucene.search.MultiPhraseQuery

lucene/queries:

• org.apache.lucene.queries.CommonTermsQuery
• org.apache.lucene.queries.CustomScoreQuery (marked as @lucene.experimental)
• org.apache.lucene.queries.mlt.MoreLikeThisQuery

lucene/suggest:

• org.apache.lucene.search.suggest.document.ContextQuery (marked as @lucene.experimental)

lucene/facet:

• org.apache.lucene.facet.DrillDownQuery (marked as @lucene.experimental)

solr/core:

• org.apache.solr.search.ExtendedQueryBase
  Several derived classes, among which:
  • org.apache.solr.query.FilterQuery
  • org.apache.solr.query.SolrRangeQuery (marked as @lucene.experimental)
  • org.apache.solr.search.RankQuery (marked in comment as experimental, but not its derived classes)
  • org.apache.solr.search.WrappedQuery
• org.apache.solr.search.join.GraphQuery (marked as @lucene.experimental)
• org.apache.solr.search.SolrConstantScoreQuery (marked in comment as experimental, but not the derived FunctionRangeQuery)