KAFKA-19345: Use ShareFetchUtils mock for DelayedShareFetchTest tests (#20765)

This patch wraps ShareFetchUtils static method `processFetchResponse`
with MockedStatic  to improve test isolation and also fixes some
incorrect test results.

Reviewers: Abhinav Dixit <[email protected]>, Andrew Schofield
 <[email protected]>

Author: brandboat

core/src/main/java/kafka/server/share/DelayedShareFetch.java

@@ -526,7 +526,6 @@ else if (isolationType == FetchIsolation.HIGH_WATERMARK)
             return offsetSnapshot.highWatermark();
         else
             return offsetSnapshot.lastStableOffset();
-
     }
 
     private LinkedHashMap<TopicIdPartition, LogReadResult> readFromLog(LinkedHashMap<TopicIdPartition, Long> topicPartitionFetchOffsets,