[SPARK-42099][SPARK-41845][CONNECT][PYTHON] Fix count(*) and count(col(*))

[zhengruifeng]

What changes were proposed in this pull request?

1, add UnresolvedStar to expressions.py;
2, Fix count(*) and count(col(*)), should return Column(UnresolvedStar(None)) instead of Column(UnresolvedAttribute("*")), see:

spark/sql/core/src/main/scala/org/apache/spark/sql/Column.scala

Lines 144 to 150 in 68531ad

	def this(name: String) = this(name match {
	case "*" => UnresolvedStar(None)
	case _ if name.endsWith(".*") =>
	val parts = UnresolvedAttribute.parseAttributeName(name.substring(0, name.length - 2))
	UnresolvedStar(Some(parts))
	case _ => UnresolvedAttribute.quotedString(name)
	})

3, remove the count(*) -> count(1) transformation in group.py, since it's no longer needed.

Why are the changes needed?

#39636 fixed the count(*) issue in the server side, and then count(expr(*)) works after that PR.

This PR makes the corresponding changes in the Python Client side, in order to support count(*), and count(col(*))

Does this PR introduce any user-facing change?

yes

How was this patch tested?

enabled UT and added UT

[zhengruifeng]

I think we should fix it in Scala side, but didn't find the right place.

[zhengruifeng]

cc @HyukjinKwon @grundprinzip @cloud-fan

[zhengruifeng]

I checked that #39636 can resolve the count(*) issue in Spark Connect.

[HyukjinKwon]

Looks fine

[dongjoon-hyun]

CI seems to complain at compilation failure. Could you double-check and re-trigger, @zhengruifeng ?

Error: SparkConnectPlannerSuite.scala:555:
value addTarget is not a member of 
org.apache.spark.connect.proto.Expression.UnresolvedStar.Builder

[dongjoon-hyun]

+1, LGTM.

[zhengruifeng]

merged into master, thank you @cloud-fan @HyukjinKwon @dongjoon-hyun !