Revert "#4693 - Drop iOS 11 support."

This reverts commit a2b359f21960e1b9f75139d94adc7aeb35fa479f.

Riot/Modules/Room/EmojiPicker/EmojiPickerViewController.swift

@@ -92,7 +92,9 @@ final class EmojiPickerViewController: UIViewController {
         
         // Enable to hide search bar on scrolling after first time view appear
         // Commenting out below code for now. It broke the navigation bar background. For details: https://github.com/vector-im/riot-ios/issues/3271
-        // self.navigationItem.hidesSearchBarWhenScrolling = true
+//        if #available(iOS 11.0, *) {
+//            self.navigationItem.hidesSearchBarWhenScrolling = true
+//        }
     }
     
     override func viewDidDisappear(_ animated: Bool) {
@@ -138,7 +140,9 @@ final class EmojiPickerViewController: UIViewController {
         
         self.setupCollectionView()
         
-        self.setupSearchController()
+        if #available(iOS 11.0, *) {
+            self.setupSearchController()
+        }
     }
     
     private func setupCollectionView() {
@@ -154,8 +158,10 @@ final class EmojiPickerViewController: UIViewController {
             collectionViewFlowLayout.sectionInset = CollectionViewLayout.sectionInsets
             collectionViewFlowLayout.sectionHeadersPinToVisibleBounds = true // Enable sticky headers
             
-            // Avoid device notch in landscape (e.g. iPhone X)
-            collectionViewFlowLayout.sectionInsetReference = .fromSafeArea
+            // Avoid device notch in landascape (e.g. iPhone X)
+            if #available(iOS 11.0, *) {
+                collectionViewFlowLayout.sectionInsetReference = .fromSafeArea
+            }
         }
         
         self.collectionView.register(supplementaryViewType: EmojiPickerHeaderView.self, ofKind: UICollectionView.elementKindSectionHeader)
@@ -169,9 +175,11 @@ final class EmojiPickerViewController: UIViewController {
         searchController.searchBar.placeholder = VectorL10n.searchDefaultPlaceholder
         searchController.hidesNavigationBarDuringPresentation = false
         
-        self.navigationItem.searchController = searchController
-        // Make the search bar visible on first view appearance
-        self.navigationItem.hidesSearchBarWhenScrolling = false
+        if #available(iOS 11.0, *) {
+            self.navigationItem.searchController = searchController
+            // Make the search bar visible on first view appearance
+            self.navigationItem.hidesSearchBarWhenScrolling = false
+        }
         
         self.definesPresentationContext = true