[SPARK-14640] Add @DeveloperApi on PythonUserDefinedType

[joan38]

What changes were proposed in this pull request?

Add @DeveloperApi on PythonUserDefinedType

[SparkQA]

Test build #55838 has finished for PR 12401 at commit ed200fd.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[andrewor14]

In general @DeveloperApis are only used for public classes. What is the motivation for adding this here?

[joan38]

@andrewor14 Sorry I've been confused by the ::DeveloperApi:: in comments.
Should we remove ::DeveloperApi:: from the scaladoc then?

[andrewor14]

Oh now I see why you did that. Yeah it doesn't even make sense to add a ::DeveloperApi:: to something without an annotation. I would remove that comment.

[joan38]

Cheers @andrewor14 for the clarification. I will do a PR for that.