Partial support for time windows (#3074)

Signed-off-by: Robert (Bobby) Evans <bobby@apache.org>

docs/configs.md

@@ -239,6 +239,7 @@ Name | SQL Function(s) | Description | Default Value | Notes
 <a name="sql.expression.Pmod"></a>spark.rapids.sql.expression.Pmod|`pmod`|Pmod|true|None|
 <a name="sql.expression.PosExplode"></a>spark.rapids.sql.expression.PosExplode|`posexplode_outer`, `posexplode`|Given an input array produces a sequence of rows for each value in the array.|true|None|
 <a name="sql.expression.Pow"></a>spark.rapids.sql.expression.Pow|`pow`, `power`|lhs ^ rhs|true|None|
+<a name="sql.expression.PreciseTimestampConversion"></a>spark.rapids.sql.expression.PreciseTimestampConversion| |Expression used internally to convert the TimestampType to Long and back without losing precision, i.e. in microseconds. Used in time windowing.|true|None|
 <a name="sql.expression.PromotePrecision"></a>spark.rapids.sql.expression.PromotePrecision| |PromotePrecision before arithmetic operations between DecimalType data|true|None|
 <a name="sql.expression.PythonUDF"></a>spark.rapids.sql.expression.PythonUDF| |UDF run in an external python process. Does not actually run on the GPU, but the transfer of data to/from it can be accelerated.|true|None|
 <a name="sql.expression.Quarter"></a>spark.rapids.sql.expression.Quarter|`quarter`|Returns the quarter of the year for date, in the range 1 to 4|true|None|