Add the array functions `ARRAY_REVERSE` / `ARRAY_MAX` / `ARRAY_MIN`

[Leomrlin]

What & why

udf/table/array/ currently has just four functions (ArrayAppend,
ArrayContains, ArrayDistinct, ArrayUnion). Adding ARRAY_REVERSE and
ARRAY_MAX / ARRAY_MIN rounds out array handling and is a nice exercise in
Java generics and edge-case thinking.

数组函数目录现在只有四个。补上 ARRAY_REVERSE(反转)、ARRAY_MAX/ARRAY_MIN(取最值),
能让数组处理更完整,也是练 Java 泛型和边界思维的好题。

The task

• array_reverse(arr) → reversed array
• array_max(arr) / array_min(arr) → max/min element (handle numeric types and null elements)

Where to look

1. There are two patterns to borrow: ArrayDistinct.java (array in → array out)
   and ArrayContains.java (array in → scalar out). Add ArrayReverse.java,
   ArrayMax.java, ArrayMin.java.
2. Register in BuildInSqlFunctionTable.java.
3. Test empty arrays, arrays with null elements, and single-element arrays.

Done when

• Three functions implemented and registered
• Empty / null-element / single-element cases clearly handled
• Your policy for null elements in array_max/min is explained in the PR
• Tests pass

[Adityaaprakash]

Hi! I'd like to work on this issue if it's still available.