fix: use qualified function identifiers for temp functions - #900

What changes were proposed in this pull request?

RandomizedContraction and KCore algorithms register temporary functions _axpb and _kcoreMerge by calling functionRegistry.registerFunction with FunctionIdentifier objects with a function name string. This PR switches registration to functionRegistry.createOrReplaceTempFunction which takes a plain name and applies the correct temporary qualifications (database and catalog) and de-registration to SessionCatalog.unregisterFunction which resolves the unqualified identifier the same way.

Why are the changes needed?

We hit this running connectedComponents using the RandomizedContraction algorithm on Spark 4.2:

[info]   java.lang.AssertionError: assertion failed: Function identifier must be fully qualified (3-part): _axpb
[info]   at scala.Predef$.assert(Predef.scala:279)
[info]   at org.apache.spark.sql.catalyst.analysis.SimpleFunctionRegistryBase.normalizeFuncName(FunctionRegistry.scala:225)
[info]   at org.apache.spark.sql.catalyst.analysis.SimpleFunctionRegistryBase.normalizeFuncName$(FunctionRegistry.scala:223)
[info]   at org.apache.spark.sql.catalyst.analysis.SimpleFunctionRegistry.normalizeFuncName(FunctionRegistry.scala:331)
[info]   at org.apache.spark.sql.catalyst.analysis.SimpleFunctionRegistryBase.registerFunction(FunctionRegistry.scala:236)
[info]   at org.apache.spark.sql.catalyst.analysis.SimpleFunctionRegistryBase.registerFunction$(FunctionRegistry.scala:232)
[info]   at org.apache.spark.sql.catalyst.analysis.SimpleFunctionRegistry.registerFunction(FunctionRegistry.scala:331)
[info]   at org.apache.spark.sql.catalyst.analysis.FunctionRegistryBase.registerFunction(FunctionRegistry.scala:71)
[info]   at org.apache.spark.sql.catalyst.analysis.FunctionRegistryBase.registerFunction$(FunctionRegistry.scala:56)
[info]   at org.apache.spark.sql.catalyst.analysis.SimpleFunctionRegistry.registerFunction(FunctionRegistry.scala:331)
[info]   ...

This can be reproduced by running the test suites using 4.2.0: ./build/sbt -Dspark.version=4.2.0 "testOnly *RandomizedContractionSuite *KCoreSuite". NOTE: I had to remove the legacy log4j.logger.* entries from core/src/test/resources/log4j2.properties in order to test on 4.2.0.

This assert statement was introduced in apache/spark#54765 to prevent unqualified functions shadowing and colliding with builtin or session functions. The change requires all function identifiers to be fully qualified with the three keys: name, database, and catalog: https://github.com/apache/spark/blob/2a7cfea06ba135cf0ddc62902eb0daf5a835c672/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala#L225

CI doesn't catch this yet because the matrix covers 3.5, 4.0, and 4.1. The fix works on all currently supported versions. createOrReplaceTempFunction registers under a plain string on 3.5/4.0/4.1 and under the qualified one on 4.2. unregisterFunction matches directly on the older versions, and on 4.2 re-qualifies via tempFunctionIdentifier when the database is empty.

I verified with testOnly *RandomizedContractionSuite *KCoreSuite against the Spark versions 3.5.8, 4.0.3, 4.1.2 and 4.2.0 and test against the versions only in the CI test matrix.