Tracking Upgrade to Datafusion 38

[Michael-J-Ward]

Upstream Changelog

Changes

Incomplete list.

• DFField was removed in refactor: make dfschema wrap schemaref datafusion#9595
• BuiltinScalarFunction was removed in Move coalesce to datafusion-functions and remove BuiltInScalarFunction datafusion#10098 along with more datafusion-functions migration
• cov_samp was moved to datafusion_functions_aggregate in Move Covariance (Sample) covar / covar_samp to be a User Defined Aggregate Function datafusion#10372

[Michael-J-Ward]

I have a functioning upgrade PR open. Once again, the guiding "design" decision was "get to compiling and passing tests" as quickly as possible.

If I removed something that you'd prefer to see implemented as a workaround, please let me know.

#691