[CALCITE-6392] Support all PostgreSQL 14 date/time patterns for to_da…

…te/to_timestamp

* First phase, mostly reorganizing classes
* Does not yet implement to_date or to_timestamp
* Fixed up fill mode handling
* Isolated the unit test class so that it can make Locale changes safely
* Introduced some new classes split out handling of some formats strings

core/src/main/java/org/apache/calcite/runtime/SqlFunctions.java

@@ -48,7 +48,7 @@
 import org.apache.calcite.util.format.FormatElement;
 import org.apache.calcite.util.format.FormatModel;
 import org.apache.calcite.util.format.FormatModels;
-import org.apache.calcite.util.format.PostgresqlDateTimeFormatter;
+import org.apache.calcite.util.format.postgresql.PostgresqlDateTimeFormatter;
 
 import org.apache.commons.codec.DecoderException;
 import org.apache.commons.codec.binary.Base32;