Add missing public initializer for SPPerspectiveShadowConfig

[niklasamslgruber]

Goal

Add public initializer to SPPerspectiveShadowConfig because currently is is impossible to create a custom configuration for the shadow since the initializer is not exposed publicly and thus leads to an error ('SPPerspectiveShadowConfig' is inaccessible due to 'internal' protection level). That is because Swift does not expose the auto-generated member-wise initializer for structs.

Source:

As with the default initializer above, if you want a public structure type to be initializable with a memberwise initializer when used in another module, you must provide a public memberwise initializer yourself as part of the type’s definition.

From: Swift.org

[ivanvorobei]

Thanks!