Iceberg java keyword column name handling

[devinrsmith]

Deephaven does not currently handle Iceberg column names that happen to be java keywords.

For example, the Iceberg column name "long" will result in a TableDefinition column name of "column_long". In this scenario though, the data is no longer properly mapped.

https://gist.github.com/devinrsmith/86b4f5fa827509df458834e7ba07ad08

[devinrsmith]

A test skeleton has been sketched out for this in io.deephaven.iceberg.PyIceberg1Test#cities2