CustomLogo final class

The site logo a theme prints, as get_custom_logo builds it (probe plugin-helpers): the custom_logo theme mod's image at full size, never lazy, its alt its own or else the site's name, linked home (marked the current page on the front page). A theme that unlinks the home page logo gets a plain span there, the image then decorative (an empty alt). The image's attributes go through get_custom_logo_image_attributes and the whole through get_custom_logo; no logo is an empty string, or in the Customizer a hidden placeholder it can fill in.