[SPARK-37219][SQL][FOLLOWUP] Make AS OF syntax more flexible

[huaxingao]

What changes were proposed in this pull request?

Make AS OF syntax more flexible

Why are the changes needed?

((FOR SYSTEM_VERSION) | VERSION) -> FOR? (SYSTEM_VERSION | VERSION) AS OF

Does this PR introduce any user-facing change?

Yes

How was this patch tested?

Existing tests

[huaxingao]

cc @cloud-fan @rdblue

[rdblue]

Thanks, @huaxingao! It would be nice to add tests for the new cases, like FOR VERSION AS OF, but I think that's minor.

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/49753/

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/49758/

[SparkQA]

Kubernetes integration test status failure
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/49753/

[SparkQA]

Kubernetes integration test status failure
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/49758/

[SparkQA]

Test build #145283 has finished for PR 34621 at commit 397102b.

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

[SparkQA]

Test build #145288 has finished for PR 34621 at commit 93cafdd.

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

[huaxingao]

Thanks for reviewing! Merged to master.