Feature: #69706 - Add support for alternative (inline) icon markup

See Issue #69706

Description

It is now possible to set alternative markups for an Icon. By default icon is rendered as <img src="..."/> tag with path to the icon file in the src attribute. With this change it’s possible to render svg icon inline in the html e.g. <svg>...</svg>.

Placing SVG images inline allows to manipulate them using CSS or JS.

$icon->setAlternativeMarkup(SvgIconProvider::MARKUP_IDENTIFIER_INLINE, '<svg>...</svg>');

Impact

An IconProvider can now add multiple markup variants for an icon.