[SPARK-48341][CONNECT] Allow plugins to use QueryTest in their tests

[tomvanbussel]

What changes were proposed in this pull request?

This PR changes QueryTest to no longer depend on RemoteSparkSession.

Why are the changes needed?

This allows the tests for Spark Connect plugin to provide their version of RemoteSparkSession (which depends on some idiosyncrasies of how Spark is built).

Does this PR introduce any user-facing change?

No

How was this patch tested?

Existing tests to ensure that nothing breaks. Manually tested that this allows a plugin to use QueryTest.

Was this patch authored or co-authored using generative AI tooling?

No

[HyukjinKwon]

Can we file a JIRA ticket please?

[HyukjinKwon]

Otherwise, seems fine.

[zhengruifeng]

the failed tests seems related:

[error] /home/runner/work/spark/spark/connector/connect/client/jvm/src/test/scala/org/apache/spark/sql/CatalogSuite.scala:29:28: illegal inheritance;
[error]  self-type org.apache.spark.sql.CatalogSuite does not conform to org.apache.spark.sql.test.RemoteSparkSession's selftype org.apache.spark.sql.test.RemoteSparkSession with org.scalatest.Suite
[error] class CatalogSuite extends RemoteSparkSession with SQLHelper {
[error]                            ^
[error] /home/runner/work/spark/spark/connector/connect/client/jvm/src/test/scala/org/apache/spark/sql/CatalogSuite.scala:31:3: package org.apache.spark.sql.test is not a value

[tomvanbussel]

@HyukjinKwon Sorry, I filed a ticket (see branch name) but forgot to include it in the PR title. (I knew I was missing something...)

@zhengruifeng Thanks, should be fixed now!

[HyukjinKwon]

Merged to master.