Give each default Spark-to-Arrow conversion its own spark.comet.convert.* config #6593

What is the problem the feature request solves?

spark.comet.sparkToColumnar.enabled and spark.comet.sparkToColumnar.supportedOperatorList decide which Spark leaf operators Comet converts to Arrow, so that the operators above them can run natively. The list is a poor interface for this:

• Its entries are Spark physical class names without the Exec suffix, and those change between Spark versions. Spark 4.1 added OneRowRelationExec. On Spark 3.4 through 4.0, Spark plans a OneRowRelation as an RDDScanExec named OneRowRelation. So the default OneRowRelation entry matches nothing there, and removing RDDScan from the list also stops converting queries such as SELECT 1.
• FileSourceScan and BatchScan only reach formats other than Parquet, JSON and CSV. Those three check spark.comet.convert.{parquet,json,csv}.enabled first.
• The default list has no effect unless spark.comet.sparkToColumnar.enabled is set, and that switch defaults to false.
• Turning on one case takes two settings. Setting the list replaces the default rather than adding to it, and names aren't validated, so a typo or a name with the Exec suffix silently does nothing.
• One switch covers several cases with different trade-offs, so no case can have its own default or its own documentation. feat: Add specific configs for converting Spark Parquet and JSON data to Arrow #832 added the per-format spark.comet.convert.* configs for the same reason, and feat: run the operators above a typed Dataset operation natively #6564 adds spark.comet.convert.typedDataset.enabled.

Describe the potential solution

Give each entry in the default list its own config, off by default, next to the per-format ones:

Keep the list for leaf operators that have no config of their own: Data Source V2 connectors (all of them are a BatchScanExec), file formats such as ORC and text, JDBC, and Hive tables. Its default becomes empty.

Deprecate the use of spark.comet.sparkToColumnar.enabled and the list for the four cases above. Until that is removed, they keep working as they do today, with a one-time warning that names the new config:

• Turning on the switch without setting the list still converts all four.
• A list that names one of them still converts it.

No default changes, so behavior stays the same until a user sets one of the new configs.

Additional context

Possible follow-ups, out of scope here:

• Turning spark.comet.convert.oneRowRelation.enabled on by default. The conversion is a single row with no columns, and it may help Spark 4.2: OneRowRelation in Union branches forces Union and downstream aggregates off Comet (TPC-DS q77a) #4949.
• Per-format configs for ORC and text (Text-format source on a broadcast build side blocks native BroadcastHashJoin #6008).
• Folding the Range conversion into spark.comet.exec.range.enabled, as the fallback when CometRangeExec declines a range.