Fixes BHV-15125

## Issue
moon.ToggleText inherited the `src` and `icon` properties from moon.Checkbox but they are not supported for this kind. As a result, the change handlers were attempting to configure a control that didn't exist in moon.ToggleText.

## Fix
Override the change handlers to no-op and mark those properties as private.

## Note
Regression from PR #1426

Enyo-DCO-1.1-Signed-off-by: Ryan Duffy <ryan.duffy@lge.com>