Add levenshtein to benchmark and update expressions.md

- Add levenshtein benchmark entry in CometStringExpressionBenchmark
- Update expressions.md to list Levenshtein as supported

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: yusinnmao

docs/source/user-guide/latest/expressions.md

@@ -66,6 +66,7 @@ of expressions that be disabled.
 | InitCap         |
 | Left            |
 | Length          |
+| Levenshtein     |
 | Like            |
 | Lower           |
 | OctetLength     |

spark/src/test/scala/org/apache/spark/sql/benchmark/CometStringExpressionBenchmark.scala

@@ -57,6 +57,8 @@ object CometStringExpressionBenchmark extends CometBenchmarkBase {
     StringExprConfig("initCap", "select initCap(c1) from parquetV1Table"),
     StringExprConfig("instr", "select instr(c1, '123') from parquetV1Table"),
     StringExprConfig("length", "select length(c1) from parquetV1Table"),
+    StringExprConfig("levenshtein", "select levenshtein(c1, 'test') from parquetV1Table"),
+    StringExprConfig("levenshtein", "select levenshtein(c1, 'test') from parquetV1Table"),
     StringExprConfig("like", "select c1 like '%123%' from parquetV1Table"),
     StringExprConfig("lower", "select lower(c1) from parquetV1Table"),
     StringExprConfig("lpad", "select lpad(c1, 150, 'x') from parquetV1Table"),