Fixed accesibility problem with <TextInput>'s Clear Button

Summary:
UITextView is accessible by default (some nested views are) and disabling that is not supported.

The problem happened because JS side sets `isAccessible` flag for UITextView and UITextField to `true` (with good intent!), which actually disables (surprise!) bult-in accessibility of TextInput on iOS.
On iOS accessible elements cannot be nested, so enabling accessibily for some container view (even in a case where this is view is a public API of TextInput on iOS) shadows some features implemented inside the component.

(Disabling accessibility of TextInput via `accessible=false` was never supported.)

Reviewed By: JoshuaGross

Differential Revision: D15280667

fbshipit-source-id: 72509b40383db6ef66c4263bd920f5ee56a42fc1

Author: shergin

Libraries/Text/TextInput/Multiline/RCTUITextView.m

@@ -58,6 +58,15 @@ - (void)dealloc
   [[NSNotificationCenter defaultCenter] removeObserver:self];
 }
 
+#pragma mark - Accessibility
+
+- (void)setIsAccessibilityElement:(BOOL)isAccessibilityElement
+{
+  // UITextView is accessible by default (some nested views are) and disabling that is not supported.
+  // On iOS accessible elements cannot be nested, therefore enabling accessibility for some container view
+  // (even in a case where this view is a part of public API of TextInput on iOS) shadows some features implemented inside the component.
+}
+
 - (NSString *)accessibilityLabel
 {
   NSMutableString *accessibilityLabel = [NSMutableString new];

Libraries/Text/TextInput/Singleline/RCTUITextField.m

@@ -43,6 +43,15 @@ - (void)_textDidChange
   _textWasPasted = NO;
 }
 
+#pragma mark - Accessibility
+
+- (void)setIsAccessibilityElement:(BOOL)isAccessibilityElement
+{
+  // UITextField is accessible by default (some nested views are) and disabling that is not supported.
+  // On iOS accessible elements cannot be nested, therefore enabling accessibility for some container view
+  // (even in a case where this view is a part of public API of TextInput on iOS) shadows some features implemented inside the component.
+}
+
 #pragma mark - Properties
 
 - (void)setTextContainerInset:(UIEdgeInsets)textContainerInset