Fix FVH boost issue (#15442)

Author: yangfeng123456

lucene/highlighter/src/java/org/apache/lucene/search/vectorhighlight/FieldPhraseList.java

@@ -177,6 +177,7 @@ public void addIfNoOverlap(WeightedPhraseInfo wpi) {
         // The result is that all informations in TermInfo are lost and not available for further
         // operations.
         existWpi.getTermsInfos().addAll(wpi.getTermsInfos());
+        existWpi.boost += wpi.getBoost(); // 累加 boost
         return;
       }
     }

lucene/highlighter/src/test/org/apache/lucene/search/vectorhighlight/TestFieldPhraseList.java

@@ -267,6 +267,25 @@ public void testToffsComparisonConsistency() {
     assertConsistentLessThan(d, b);
     assertConsistentLessThan(d, c);
   }
+  public void testMergeOverlappingWeightedPhraseInfoAccumulateBoost() {
+    LinkedList<TermInfo> infos1 = new LinkedList<>();
+    infos1.add(new TermInfo("中国", 0, 2, 0, 0));
+    infos1.add(new TermInfo("经济", 3, 5, 1, 1));
+    WeightedPhraseInfo wpi1 = new WeightedPhraseInfo(infos1, 2.0f);
+
+    LinkedList<TermInfo> infos2 = new LinkedList<>();
+    infos2.add(new TermInfo("经济", 3, 5, 1, 1));
+    infos2.add(new TermInfo("发展", 6, 8, 2, 2));
+    WeightedPhraseInfo wpi2 = new WeightedPhraseInfo(infos2, 3.0f);
+
+    // trigger merge
+    WeightedPhraseInfo merged =
+            new WeightedPhraseInfo(java.util.List.of(wpi1, wpi2));
+
+    assertEquals(5.0f, merged.getBoost(), 0.0001f);
+  }
+
+
 
   private WeightedPhraseInfo newInfo(int startOffset, int endOffset, float boost) {
     LinkedList<TermInfo> infos = new LinkedList<>();