git cherry-pick escape fix to 0.63-stable branch (#722)

* Add nullability checks (#704)

* Update RCTCxxBridge.mm

* add nullability checks

* Change key identifier from "Esc" -> "Escape" (#720)

Co-authored-by: Scott Kyle <scott@appden.com>

Author: HeyImChris

RNTester/js/examples/KeyboardEventsExample/KeyboardEventsExample.js

@@ -54,7 +54,7 @@ class KeyEventExample extends React.Component<{}, State> {
             <View
               acceptsKeyboardFocus={true}
               enableFocusRing={true}
-              validKeysDown={['g', 'Esc', 'Enter', 'ArrowLeft']}
+              validKeysDown={['g', 'Escape', 'Enter', 'ArrowLeft']}
               onKeyDown={this.onKeyDownEvent}
               validKeysUp={['c', 'd']}
               onKeyUp={this.onKeyUpEvent}>

React/Views/RCTView.m

@@ -1688,7 +1688,7 @@ - (NSString*)keyIsValid:(NSString*)key left:(BOOL)leftArrowPressed right:(BOOL)r
   BOOL downArrowValidityCheck = [validKeys containsObject:downArrowPressKey] && downArrowPressed;
 
   if (escapeKeyValidityCheck) {
-    keyToReturn = @"Esc";
+    keyToReturn = @"Escape";
   } else if (enterKeyValidityCheck) {
     keyToReturn = @"Enter";
   } else if (leftArrowValidityCheck) {