Add GpuConv operator for the conv 10<->16 expression (#8925)

Contributes to #8511 

POC only supports 10/16<->10/16 radix conversions, without overflow checks it's guaranteed to produce identical results to CPU only for 
- decimal strings not longer than 18 characters 
- hexadecimal strings not longer than 15 characters 

Signed-off-by: Gera Shegalov <gera@apache.org>

docs/additional-functionality/advanced_configs.md

@@ -208,6 +208,7 @@ Name | SQL Function(s) | Description | Default Value | Notes
 <a name="sql.expression.Concat"></a>spark.rapids.sql.expression.Concat|`concat`|List/String concatenate|true|None|
 <a name="sql.expression.ConcatWs"></a>spark.rapids.sql.expression.ConcatWs|`concat_ws`|Concatenates multiple input strings or array of strings into a single string using a given separator|true|None|
 <a name="sql.expression.Contains"></a>spark.rapids.sql.expression.Contains| |Contains|true|None|
+<a name="sql.expression.Conv"></a>spark.rapids.sql.expression.Conv|`conv`|Convert string representing a number from one base to another|false|This is disabled by default because GPU implementation is incomplete. We currently only support from/to_base values of 10 and 16. We fall back on CPU if the signed conversion is signalled via a negative to_base. GPU implementation does not check for an 64-bit signed/unsigned int overflow when performing the conversion to return `FFFFFFFFFFFFFFFF` or `18446744073709551615` or to throw an error in the ANSI mode. It is safe to enable if the overflow is not possible or detected externally. For instance decimal strings not longer than 18 characters / hexadecimal strings not longer than 15 characters disregarding the sign cannot cause an overflow.          |
 <a name="sql.expression.Cos"></a>spark.rapids.sql.expression.Cos|`cos`|Cosine|true|None|
 <a name="sql.expression.Cosh"></a>spark.rapids.sql.expression.Cosh|`cosh`|Hyperbolic cosine|true|None|
 <a name="sql.expression.Cot"></a>spark.rapids.sql.expression.Cot|`cot`|Cotangent|true|None|