[SEDONA-522] Add ST_Union with array of Geometry as input

[furqaankhan]

Did you read the Contributor Guide?

• Yes, I have read Contributor Rules and Contributor Development Guide

Is this PR related to a JIRA ticket?

• Yes, the URL of the associated JIRA ticket is https://issues.apache.org/jira/browse/SEDONA-522. The PR name follows the format [SEDONA-XXX] my subject.

What changes were proposed in this PR?

• Add ST_Union with Array input
• Port ST_Union with 2 geometry input to Flink

How was this patch tested?

• Passed new and existing tests

Did this PR include necessary documentation updates?

• Yes, I have updated the documentation update.

[jiayuasu]

1. Can you also update the ST_H3toGeom and ST_S2toGeom doc to explain how this ST_Union works in conjunction with these functions?

2. What happens to polygons that could not be unioned (polygons that share no boundaries)?

[furqaankhan]

1. Sure.
2. It returns a MultiPolygon with each set of boundaries. See here:

   sedona/spark/common/src/test/scala/org/apache/sedona/sql/functionTestScala.scala

   Lines 700 to 705 in ec6dfff

   	it("Passed ST_Union - array variant") {
   	val polyDf = sparkSession.sql("select array(ST_GeomFromWKT('POLYGON ((-3 -3, 3 -3, 3 3, -3 3, -3 -3))'),ST_GeomFromWKT('POLYGON ((5 -3, 7 -3, 7 -1, 5 -1, 5 -3))'), ST_GeomFromWKT('POLYGON((4 4, 4 6, 6 6, 6 4, 4 4))')) as polys")
   	val actual = polyDf.selectExpr("ST_Union(polys)").take(1)(0).get(0).asInstanceOf[Geometry].toText
   	val expected = "MULTIPOLYGON (((5 -3, 5 -1, 7 -1, 7 -3, 5 -3)), ((-3 -3, -3 3, 3 3, 3 -3, -3 -3)), ((4 4, 4 6, 6 6, 6 4, 4 4)))"
   	assert(expected.equals(actual))
   	}

[jiayuasu]

@furqaankhan Cool. Can you also explain this in the doc?

[jiayuasu]

@furqaankhan Cool. Can you also explain this in the doc?