Add method to take clauses out of boolean query

This helps with rewriting, for example to replace the default
score combiner used by boolean queries, insofer it avoids
the need to `box_clone` the sub queries.

Author: Adam Reichold

src/query/boolean_query/boolean_query.rs

@@ -1,3 +1,5 @@
+use std::mem;
+
 use super::boolean_weight::BooleanWeight;
 use crate::query::{EnableScoring, Occur, Query, SumCombiner, TermQuery, Weight};
 use crate::schema::{IndexRecordOption, Term};
@@ -257,6 +259,11 @@ impl BooleanQuery {
     pub fn clauses(&self) -> &[(Occur, Box<dyn Query>)] {
         &self.subqueries[..]
     }
+
+    /// Take the clauses making up this query for reuse.
+    pub fn take_clauses(&mut self) -> Vec<(Occur, Box<dyn Query>)> {
+        mem::take(&mut self.subqueries)
+    }
 }
 
 #[cfg(test)]