Fix an issue where buttons in text overlay toolbar could be too small.

The cause of this issue was that ImageEditorViewController's view was created
with zero dimensions. Those dimensions were then used to pre-calculate size
of the toolbar which ended up being incorrect.

The fix is to let UIKit create the root view and move everything we did in `loadView`
to `viewDidLoad`.

SignalUI/Views/ImageEditor/ImageEditorViewController.swift

@@ -234,10 +234,8 @@ class ImageEditorViewController: OWSViewController {
         model.add(observer: self)
     }
 
-    override func loadView() {
-        view = UIView()
+    override func viewDidLoad() {
         view.backgroundColor = .black
-        view.isOpaque = true
 
         imageEditorView.configureSubviews()
         view.addSubview(imageEditorView)
@@ -268,10 +266,6 @@ class ImageEditorViewController: OWSViewController {
         strokeWidthSliderPosition = strokeWidthSliderContainer.centerXAnchor.constraint(equalTo: view.leadingAnchor)
         strokeWidthSliderPosition?.autoInstall()
         strokeWidthSliderContainer.addGestureRecognizer(UITapGestureRecognizer(target: self, action: #selector(handleSliderContainerTap(_:))))
-    }
-
-    override func viewDidLoad() {
-        super.viewDidLoad()
 
         updateUIForCurrentMode()
     }