[GH-2830] Adds Geography dual-dispatch to ST_Area

[zhangfengcdt]

Did you read the Contributor Guide?

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

Is this PR related to a ticket?

• Yes, and the PR name follows the format [GH-XXX] my subject. Closes #<issue_number>

What changes were proposed in this PR?

• Adds Geography dual-dispatch to ST_Area — returns geodesic area in square meters on the WGS84 spheroid for Geography inputs.
• Using S2 library to calculate the area on sphere directly.

How was this patch tested?

• mvn clean test -pl common -am -Dtest=FunctionTest
• New Spark SQL cases in GeographyFunctionTest
• mvn spotless:apply run before commit; no format violations.

Did this PR include necessary documentation updates?

• Yes, I have updated the documentation.

[Copilot]

Pull request overview

Adds Geography dual-dispatch support for ST_Area so Geography inputs return geodesic area (m²) on the WGS84 spheroid, aligning with existing Geography metric behavior (e.g., ST_Distance).

Changes:

• Add org.apache.sedona.common.geography.Functions.area(Geography) backed by Spheroid.area(JTS).
• Enable Spark SQL ST_Area expression to resolve to either Geometry-area or Geography-area implementation based on input type.
• Add/extend unit + Spark SQL integration tests and document the Geography ST_Area function.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
spark/common/src/main/scala/org/apache/spark/sql/sedona_sql/expressions/Functions.scala	Adds dual-dispatch resolution for ST_Area (Geometry vs Geography).
common/src/main/java/org/apache/sedona/common/geography/Functions.java	Introduces Geography area implementation using spheroid/geodesic area calculation.
spark/common/src/test/scala/org/apache/sedona/sql/geography/GeographyFunctionTest.scala	Adds Spark SQL integration tests for ST_Area on Geography inputs.
common/src/test/java/org/apache/sedona/common/Geography/FunctionTest.java	Adds unit tests for Geography Functions.area behavior (polygon/point/linestring/null).
docs/api/sql/geography/Geography-Functions/ST_Area.md	Adds Geography API documentation for ST_Area.
docs/api/sql/geography/Geography-Functions.md	Adds ST_Area to the Geography functions index.

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