[SPARK-27951][SQL][FOLLOWUP] Improve the window function nth_value

[beliefer]

What changes were proposed in this pull request?

#29604 supports the ANSI SQL NTH_VALUE.
We should override the prettyName and sql.

Why are the changes needed?

Make the name of nth_value correct.
To show the ignoreNulls parameter correctly.

Does this PR introduce any user-facing change?

'No'.

How was this patch tested?

Jenkins test.

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33778/

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33778/

[SparkQA]

Test build #129163 has finished for PR 29886 at commit 7f3c033.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #129167 has finished for PR 29886 at commit fe9b8ab.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #129166 has finished for PR 29886 at commit 7393082.

• This patch fails due to an unknown error code, -9.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33781/

[HyukjinKwon]

retest this please

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33781/

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33782/

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33782/

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33785/

[SparkQA]

Kubernetes integration test status failure
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/33785/

[SparkQA]

Test build #129170 has finished for PR 29886 at commit fe9b8ab.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

Merged to master.

[beliefer]

@HyukjinKwon @cloud-fan Thanks!