[SPARK-48766][PYTHON] Document the behavior difference of `extraction…

…` between `element_at` and `try_element_at`

### What changes were proposed in this pull request?
Document the behavior difference of `extraction` between `element_at` and `try_element_at`

### Why are the changes needed?
when the function `try_element_at` was introduced in 3.5, its `extraction` handling was unintentionally  not consistent with the `element_at`, which causes confusion.

This PR document this behavior difference (I don't think we can fix it since it will be a breaking change).
```
In [1]: from pyspark.sql import functions as sf

In [2]: df = spark.createDataFrame([({"a": 1.0, "b": 2.0}, "a")], ['data', 'b'])

In [3]: df.select(sf.try_element_at(df.data, 'b')).show()
+-----------------------+
|try_element_at(data, b)|
+-----------------------+
|                    1.0|
+-----------------------+

In [4]: df.select(sf.element_at(df.data, 'b')).show()
+-------------------+
|element_at(data, b)|
+-------------------+
|                2.0|
+-------------------+
```

### Does this PR introduce _any_ user-facing change?
doc changes

### How was this patch tested?
ci, added doctests

### Was this patch authored or co-authored using generative AI tooling?
no

Closes apache#47161 from zhengruifeng/doc_element_at_extraction.

Authored-by: Ruifeng Zheng <ruifengz@apache.org>
Signed-off-by: Ruifeng Zheng <ruifengz@apache.org>

python/pyspark/sql/functions/builtin.py

@@ -14098,10 +14098,13 @@ def element_at(col: "ColumnOrName", extraction: Any) -> Column:
     Notes
     -----
     The position is not zero based, but 1 based index.
+    If extraction is a string, :meth:`element_at` treats it as a literal string,
+    while :meth:`try_element_at` treats it as a column name.
 
     See Also
     --------
     :meth:`get`
+    :meth:`try_element_at`
 
     Examples
     --------
@@ -14148,6 +14151,17 @@ def element_at(col: "ColumnOrName", extraction: Any) -> Column:
     +-------------------+
     |               NULL|
     +-------------------+
+
+    Example 5: Getting a value from a map using a literal string as the key
+
+    >>> from pyspark.sql import functions as sf
+    >>> df = spark.createDataFrame([({"a": 1.0, "b": 2.0}, "a")], ['data', 'b'])
+    >>> df.select(sf.element_at(df.data, 'b')).show()
+    +-------------------+
+    |element_at(data, b)|
+    +-------------------+
+    |                2.0|
+    +-------------------+
     """
     return _invoke_function_over_columns("element_at", col, lit(extraction))
 
@@ -14172,6 +14186,17 @@ def try_element_at(col: "ColumnOrName", extraction: "ColumnOrName") -> Column:
     extraction :
         index to check for in array or key to check for in map
 
+    Notes
+    -----
+    The position is not zero based, but 1 based index.
+    If extraction is a string, :meth:`try_element_at` treats it as a column name,
+    while :meth:`element_at` treats it as a literal string.
+
+    See Also
+    --------
+    :meth:`get`
+    :meth:`element_at`
+
     Examples
     --------
     Example 1: Getting the first element of an array
@@ -14228,6 +14253,17 @@ def try_element_at(col: "ColumnOrName", extraction: "ColumnOrName") -> Column:
     +-----------------------+
     |                   NULL|
     +-----------------------+
+
+    Example 6: Getting a value from a map using a column name as the key
+
+    >>> from pyspark.sql import functions as sf
+    >>> df = spark.createDataFrame([({"a": 1.0, "b": 2.0}, "a")], ['data', 'b'])
+    >>> df.select(sf.try_element_at(df.data, 'b')).show()
+    +-----------------------+
+    |try_element_at(data, b)|
+    +-----------------------+
+    |                    1.0|
+    +-----------------------+
     """
     return _invoke_function_over_columns("try_element_at", col, extraction)