[GH-3202] Handle empty Geography inputs in ST_MakeLine

[jiayuasu]

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 [BUG]: Geography ST_MakeLine fails on empty inputs #3202.

What changes were proposed in this PR?

• Ignore empty Point, MultiPoint, and LineString components when assembling a Geography LineString.
• Return LINESTRING EMPTY when neither input contributes a coordinate.
• Duplicate the remaining coordinate when exactly one coordinate survives, producing a valid zero-length JTS/OGC LineString with the same point set.
• Preserve the existing first-input SRID behavior.
• Document the empty-input contract for Spark and Flink.

PostGIS and SedonaDB skip empty components but can represent or emit a one-coordinate LineString. JTS rejects that representation, so duplicating the sole coordinate is the valid-JTS adaptation.

How was this patch tested?

• Common Geography function suite: 87 tests, 0 failures.
• Spark Geography function suite: 55 tests, 0 failures.
• Flink Geography function suite: 18 tests, 0 failures.
• Coverage includes empty Point, MultiPoint, and LineString inputs, one surviving coordinate in either position, both inputs empty, WKB round trips, and first-input SRID preservation.
• All cross-module tests used a task-isolated Maven repository to avoid SNAPSHOT artifact contamination.
• Spotless, commit hooks, and diff checks passed.

Did this PR include necessary documentation updates?

• Yes. The Spark and Flink Geography ST_MakeLine pages document how empty inputs and a single surviving coordinate are handled.