[fenix] Fixes https://github.com/mozilla-mobile/fenix/issues/6341: Initialize 'selectedTabs' based on opened/selected tabs.

The problem was that the parameter 'selectedTabIds' was not taken into account
when initializing the variable 'selectedTabs'. So I made the initialization
based on both the selected tab and the number of open tabs.

app/src/main/java/org/mozilla/fenix/collections/CollectionCreationFragment.kt

@@ -47,7 +47,12 @@ class CollectionCreationFragment : DialogFragment() {
         val sessionManager = requireComponents.core.sessionManager
         val publicSuffixList = requireComponents.publicSuffixList
         val tabs = sessionManager.getTabs(args.tabIds, publicSuffixList)
-        val selectedTabs = if (tabs.size == 1) setOf(tabs.first()) else emptySet()
+        val selectedTabs = if (args.selectedTabIds != null) {
+            sessionManager.getTabs(args.selectedTabIds, publicSuffixList).toSet()
+        } else {
+            if (tabs.size == 1) setOf(tabs.first()) else emptySet()
+        }
+
         val tabCollections = requireComponents.core.tabCollectionStorage.cachedTabCollections
         val selectedTabCollection = args.selectedTabCollectionId
             .let { id -> tabCollections.firstOrNull { it.id == id } }