Function isSubtypeSublayerExtension

isSubtypeSublayerExtension(extension): extension is SubtypeSublayerExtension<SubtypeSublayerExtensionProperties>
Returns true if the extension is a SubtypeSublayerExtension.
Parameters
- extension: unknown
  The extension to check.
Returns extension is SubtypeSublayerExtension<SubtypeSublayerExtensionProperties>