Implement ST_MakeBox2D(p1, p2) scalar constructor

[jiayuasu]

Sub-task of #2877.

Scope

Add the ST_MakeBox2D(lower_left: Point, upper_right: Point) -> Box2D scalar constructor. Direct PostGIS counterpart.

Returns a Box2D from two opposing corner points. NULL propagates from either input.

Implementation

• New ST_MakeBox2D case class in spark/common/.../expressions/Constructors.scala.
• Backing helper in common/.../Functions.java (or a new Box2DConstructors.java) that builds a Box2D from two Point instances.
• Catalog registration.
• Tests: ordered corners, swapped corners (xmin > xmax should remain — this is the antimeridian-reserved space, NOT empty; document the user contract), 3D point input, null propagation.

Out of scope

ST_3DMakeBox (waits for Box3D).