/**
* @callback Phaser.Types.GameObjects.Particles.EdgeZoneSourceCallback
* @since 3.0.0
*
* @param {number} quantity - The number of particles to place on the source edge. If 0, `stepRate` should be used instead.
* @param {number} [stepRate] - The distance between each particle. When set, `quantity` is implied and should be set to `0`.
*
* @return {Phaser.Types.Math.Vector2Like[]} - The points placed on the source edge.
*/