[SPARK-37483][SQL][FOLLOWUP] Rename pushedTopN to PushedTopN and …

…improve JDBCV2Suite

### What changes were proposed in this pull request?
This PR fix three issues.
**First**, create method `checkPushedInfo` and `checkSortRemoved` to reuse code.
**Second**, remove method `checkPushedLimit`, because `checkPushedInfo` can cover it.
**Third**, rename `pushedTopN` to `PushedTopN`, so as consistent with other pushed information.

### Why are the changes needed?
Reuse code and let pushed information more correctly.

### Does this PR introduce _any_ user-facing change?
'No'. New feature and improve the tests.

### How was this patch tested?
Adjust existing tests.

Closes #35921 from beliefer/SPARK-37483_followup.

Authored-by: Jiaan Geng <beliefer@163.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
(cherry picked from commit 4fe55c5)
Signed-off-by: Wenchen Fan <wenchen@databricks.com>

sql/core/src/main/scala/org/apache/spark/sql/execution/DataSourceScanExec.scala

@@ -148,7 +148,7 @@ case class RowDataSourceScanExec(
         val pushedTopN =
           s"ORDER BY ${seqToString(pushedDownOperators.sortValues.map(_.describe()))}" +
           s" LIMIT ${pushedDownOperators.limit.get}"
-        Some("pushedTopN" -> pushedTopN)
+        Some("PushedTopN" -> pushedTopN)
     } else {
       pushedDownOperators.limit.map(value => "PushedLimit" -> s"LIMIT $value")
     }