@protocol MDCLeadingViewTextInput <MDCTextInput>
Common API for text inputs that support having a leading view.
MDCTextField implements this protocol but MDCMultilineTextField does not because the designers determined multiline text fields should only have trailing views.
An overlay view on the leading side.
Note: if RTL is engaged, this will return the .rightView and if LTR, it will return the .leftView.
@property (nonatomic, strong, readwrite, nullable) UIView *leadingView;
Controls when the leading view will display.
@property (nonatomic, assign, unsafe_unretained, readwrite) UITextFieldViewMode leadingViewMode;