[Coral-Trino] Remove characters sets from TrinoSqlDialect

[KevinGe00]

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

Previously, charSetName was dropped from VARCHAR/CHAR fields when a Coral RelNode is being converted to a Trino SqlNode. This happened by overriding supportsCharSet to be false in TrinoSqlDialect. As art of merging TrinoSqlDialect -> CoralSqlDialect, we want TrinoSqlDialect to match CoralSqlDialect meaning the override needed to be undone.

Now, charSetName is instead dropped from VARCHAR/CHAR fields dropped as part of SqlNode rewriting in TrinoSqlRewriter by adding a datatype replacement rule.

How was this patch tested?

1. clean build
2. new unit test to test character sets are removed in CAST calls that are nested
3. i-test passed

[aastha25]

thanks for the PR @KevinGe00!
Please add an example in the description elaborating the previous and newer workflow - that charSetName was dropped from VARCHAR/CHAR fields when Coral RelNode converted to Trino SqlNode. Now it is dropped as part of SqlNode rewriting.