Fix ImageViewer: Apply applyDefaultHierarchyTemplate (#4762)

The intermediate `iosMain` source was previously removed here:
https://github.com/JetBrains/compose-multiplatform/pull/3956 And it
worked fine.

According to the doc
https://kotlinlang.org/docs/whatsnew1920.html#set-up-the-target-hierarchy
:
> If you want to have additional source sets that the default hierarchy
template doesn't provide, for example, one that shares code between a
macOS and a JVM target, adjust the hierarchy by reapplying the template
explicitly with applyDefaultHierarchyTemplate() and configuring
additional source sets manually as usual with dependsOn()

Now we have an additional custom source set named 'jsWasmMain',
therefore we need to have `applyDefaultHierarchyTemplate()`.

examples/imageviewer/shared/build.gradle.kts

@@ -28,6 +28,8 @@ kotlin {
         }
     }
 
+    applyDefaultHierarchyTemplate()
+
     sourceSets {
         all {
             languageSettings {