Added perPage property on Siema (#40451)

* Added perPage property

Siema makes the property perPage available, and it is useful to be able to read it, so I'm adding it to the type definition.

* added test

* added myself as contributor

* fixed tests

types/siema/index.d.ts

@@ -3,10 +3,12 @@
 // Definitions by: Irmantas Zenkus <https://github.com/Irmiz>
 //                 Pavel Puchkov <https://github.com/0x6368656174>
 //                 Sam Nau <https://github.com/samnau>
+//                 Jonathan Loss <https://github.com/barroudjo>
 // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
 
 export default class Siema {
     currentSlide: number;
+    perPage: number;
 
     constructor(options?: SiemaOptions);
 

types/siema/siema-tests.ts

@@ -25,3 +25,4 @@ siema.prepend(elem, () => {});
 siema.append(elem, () => {});
 siema.destroy();
 siema.destroy(true, () => {});
+siema.goTo(siema.perPage);