feat(ios): use PHPickerViewController for iOS 14+ (#937)

- Does not need any permissions for reading images
- The PHPickerViewController class is an alternative to UIImagePickerController. PHPickerViewController improves stability and reliability, and includes several benefits to developers and users, such as the following:
- Deferred image loading and recovery UI
- Reliable handling of large and complex assets, like RAW and panoramic images
- User-selectable assets that aren’t available for UIImagePickerController
- Configuration of the picker to display only Live Photos
- Availability of PHLivePhoto objects without library access
- Stricter validations against invalid inputs
- See documentation of PHPickerViewController: https://developer.apple.com/documentation/photosui/phpickerviewcontroller?language=objc
- Added tests for PHPickerViewController in `CameraTest.m`

* Documentation and formatting

- Document `takePicture` and `showCameraPicker` in `CDVCamera.m`
- A pragmas for UIImagePickerControllerDelegate methods and CLLocationManager methods
- Format some long methods declarations to multi-line instead single-line for better readability
- Remove unnecessry `dispatch_async(dispatch_get_main_queue() ...` in `takePicture` before calling `showCameraPicker`. This is already done in `showCameraPicker`.
- Source out code for permission denied alert dialog when accessing the camera or UIImagePickerController on iOS < 14 for picking images

* feat(ios): proper formatting of methods

- Use linux brace style: A brace have to be on a new line for method declarations
- Remove unnecessary whitespaces in method declrations

* doc: readme update

- Better document usage descriptions
- `NSPhotoLibraryUsageDescription` not needed for iOS 14+ when only picking images
- Improve formatting for xml, js
- sourceType `SAVEDPHOTOALBUM` is the same as `PHOTOLIBRARY` on Android and iOS 14+
- Use `PHOTOLIBRARY` as sourceType instead of `SAVEDPHOTOALBUM` in  photo picker example

* Android: Document `SAVEDPHOTOALBUM``

- Make clear that `SAVEDPHOTOALBUM` is the same like `PHOTOLIBRARY` and has only an effect on iOS < 14
- Format code when creating image chooser and document the request code parameter

src/android/CameraLauncher.java

@@ -77,9 +77,10 @@ public class CameraLauncher extends CordovaPlugin implements MediaScannerConnect
     private static final int DATA_URL = 0;              // Return base64 encoded string
     private static final int FILE_URI = 1;              // Return file uri (content://media/external/images/media/2 for Android)
 
-    private static final int PHOTOLIBRARY = 0;          // Choose image from picture library (same as SAVEDPHOTOALBUM for Android)
+    private static final int PHOTOLIBRARY = 0;          // Choose image from picture library
     private static final int CAMERA = 1;                // Take picture from camera
-    private static final int SAVEDPHOTOALBUM = 2;       // Choose image from picture library (same as PHOTOLIBRARY for Android)
+    private static final int SAVEDPHOTOALBUM = 2;       // Same as PHOTOLIBRARY. This settings makes only a difference on iOS older than 14,
+                                                        // where an image can only be chosen from the device's Camera Roll album, with this setting.
 
     private static final int PICTURE = 0;               // allow selection of still pictures only. DEFAULT. Will return format specified via DestinationType
     private static final int VIDEO = 1;                 // allow selection of video only, ONLY RETURNS URL
@@ -423,9 +424,15 @@ public class CameraLauncher extends CordovaPlugin implements MediaScannerConnect
             intent.setAction(Intent.ACTION_GET_CONTENT);
             intent.addCategory(Intent.CATEGORY_OPENABLE);
         }
+
         if (this.cordova != null) {
-            this.cordova.startActivityForResult((CordovaPlugin) this, Intent.createChooser(intent,
-                    new String(title)), (srcType + 1) * 16 + returnType + 1);
+            this.cordova.startActivityForResult(
+                (CordovaPlugin) this,
+                Intent.createChooser(
+                    intent,
+                    new String(title)),
+                    // Requestcode
+                    (srcType + 1) * 16 + returnType + 1);
         }
     }