title: readOnly is not applying for input field of KeyboardDatePicker of material ui in react js
body: <p>KeyboardDatePicker is not supporting readOnly property for its input field</p>
  
  <p>I tried readOnly property which already mentioned in API document, but its not worked out. It is applying readOnly for parent container not for the input field in KeyboardDatePicker.</p>
  
  <pre><code>&lt;KeyboardDatePicker
      margin="normal"
      id="mui-pickers-date"
      className = "dialog-calendar"
      value={selectedDate}
      shouldDisableDate = {handleDisableDate}
      minDate = {startDate}
      maxDate = {endDate}
      minDateMessage = ''
      onChange={handleDateChange}
      format = "MM/dd/yyyy"
      disablePast = {true}
      disabled = {isDisabled}
      allowKeyboardControl = {false}
      readOnly = {true}
      autoFill = {false}
      KeyboardButtonProps={{
           'aria-label': 'change date',
      }}
  </code></pre>