Function favicon
Sets the favicon, which is the icon typically displayed in the browser tab or address bar. It searches for the icon in the following priority: 1. Use the icon set in the Customizer. 2. Look in the child theme folder for favicon.png, .ico, or .gif. 3. Look in the parent theme folder for favicon.png, .ico, or .gif.
Note: The markup that is generated and echoed in this function is a <link> element that goes into the <head> block.