[SPARK-31474][SQL][FOLLOWUP] Replace _FUNC_ placeholder with functionname in the note field of expression info

### What changes were proposed in this pull request?

\_FUNC\_ is used in note() of `ExpressionDescription` since https://github.com/apache/spark/pull/28248, it can be more cases later, we should replace it with function name for documentation

### Why are the changes needed?

doc fix

### Does this PR introduce any user-facing change?

no

### How was this patch tested?

pass Jenkins, and verify locally with Jekyll serve

Closes #28305 from yaooqinn/SPARK-31474-F.

Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>

sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/ExpressionDescription.java

@@ -79,8 +79,8 @@ import java.lang.annotation.RetentionPolicy;
  * </code>
  * </pre>
  *
- *  We can refer the function name by `_FUNC_`, in `usage()`, `arguments()` and `examples()` as
- *  it is registered in `FunctionRegistry`.
+ *  We can refer the function name by `_FUNC_`, in `usage()`, `arguments()`, `examples()` and
+ *  `note()` as it is registered in `FunctionRegistry`.
  *
  *  Note that, if `extended()` is defined, `arguments()`, `examples()`, `note()`, `group()`,
  *  `since()` and `deprecated()` should be not defined together. `extended()` exists

sql/gen-sql-api-docs.py

@@ -43,7 +43,7 @@ def _list_function_infos(jvm):
             usage=usage,
             arguments=jinfo.getArguments().replace("_FUNC_", name),
             examples=jinfo.getExamples().replace("_FUNC_", name),
-            note=jinfo.getNote(),
+            note=jinfo.getNote().replace("_FUNC_", name),
             since=jinfo.getSince(),
             deprecated=jinfo.getDeprecated()))
     return sorted(infos, key=lambda i: i.name)