Replace FunctionFieldReferenceOperator with Calcite DOT operator

[KevinGe00]

What changes are proposed in this pull request, and why are they necessary?

We can get rid of FunctionFieldReferenceOperator entirely and replace it with Calcite's default SqlDotOperator. Historically FunctionFieldReferenceOperator was introduced because "Calcite DOT operator by default does not work for referencing fields from struct return types of functions." However, that's no longer the case, thus rendering FunctionFieldReferenceOperator unneeded. If we can get rid of FunctionFieldReferenceOperator, we also no longer need to migrate it (as part of Coral IR upgrades).

How was this patch tested?

• clean build
• ran regression tests for avro, trino and spark
  Only regression I'm seeing is a cosmetic one that is actually desirable. Unnecessary parentheses introduced because FunctionFieldReferenceOperator is not a native Calcite operator go away:

old: (coalesce_struct(table.struct_col).tag_1).field
new: coalesce_struct(table.struct_col).tag_1.field

[aastha25]

1. Have we verified that the cosmetic changes have no impact when queried on Spark/Trino? This should be a simple experiment to execute the two variants on Spark/Trino for a sample table.

2. Could you also confirm the the RelNode representations have no differences apart from the operator name?