Stub for `clearButtonMode` prop in RCTUITextView

Summary: Even if we don't support this prop yet, we have to expose this in RCTUITextView to conform the contract between ViewManager and ShadowView.

Reviewed By: sahrens

Differential Revision: D6842304

fbshipit-source-id: 7ea26974f595eba6a3c06df06ca01e46af2e63df

Libraries/Text/TextInput/Multiline/RCTUITextView.h

@@ -31,6 +31,10 @@ NS_ASSUME_NONNULL_BEGIN
 
 @property (nonatomic, assign) CGFloat preferredMaxLayoutWidth;
 
+// The `clearButtonMode` property actually is not supported yet;
+// it's declared here only to conform to the interface.
+@property (nonatomic, assign) UITextFieldViewMode clearButtonMode;
+
 @end
 
 NS_ASSUME_NONNULL_END