[SPARK-35459][SQL][TESTS] Move AvroRowReaderSuite to a separate file

[MaxGekk]

What changes were proposed in this pull request?

Move AvroRowReaderSuite out from AvroSuite.scala and place it to AvroRowReaderSuite.scala.

Why are the changes needed?

To improve code maintenance. Usually, independent test suites are placed to separate files.

Does this PR introduce any user-facing change?

No

How was this patch tested?

By running the affected test suites:

$ build/sbt "test:testOnly *AvroRowReaderSuite"
$ build/sbt "test:testOnly *AvroV1Suite"
$ build/sbt "test:testOnly *AvroV2Suite"

[SparkQA]

Test build #138743 has finished for PR 32607 at commit 1d1f246.

• This patch passes all tests.
• 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/43265/

[HyukjinKwon]

Merged to master.

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/43265/

[dongjoon-hyun]

+1, LGTM.