Add getter for SynonymQuery#field (#13077)

---------

Co-authored-by: Andrey Bozhko <abozhko@apple.com>

lucene/CHANGES.txt

@@ -178,6 +178,8 @@ Other
 
 * GITHUB#13001: Put Thread#sleep() on the list of forbidden APIs. (Shubham Chaudhary)
 
+* GITHUB#13077: Add public getter for SynonymQuery#field (Andrey Bozhko)
+
 ======================== Lucene 9.11.0 =======================
 
 API Changes

lucene/core/src/java/org/apache/lucene/search/SynonymQuery.java

@@ -115,10 +115,16 @@ public final class SynonymQuery extends Query {
     this.field = Objects.requireNonNull(field);
   }
 
+  /** Returns the terms of this {@link SynonymQuery} */
   public List<Term> getTerms() {
     return Arrays.stream(terms).map(t -> new Term(field, t.term)).toList();
   }
 
+  /** Returns the field name of this {@link SynonymQuery} */
+  public String getField() {
+    return field;
+  }
+
   @Override
   public String toString(String field) {
     StringBuilder builder = new StringBuilder("Synonym(");

lucene/core/src/test/org/apache/lucene/search/TestSynonymQuery.java

@@ -87,6 +87,12 @@ public class TestSynonymQuery extends LuceneTestCase {
         new SynonymQuery.Builder("field2").addTerm(new Term("field2", "b"), 0.4f).build());
   }
 
+  public void testGetField() {
+    SynonymQuery query =
+        new SynonymQuery.Builder("field1").addTerm(new Term("field1", "a")).build();
+    assertEquals("field1", query.getField());
+  }
+
   public void testBogusParams() {
     expectThrows(
         IllegalArgumentException.class,