Support any GUI system to HTML binding

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Now project can support any GUI via custom cobalt html nodes.

Some ideas:

• add html/css support to IMGUI
• add html/css support QT widgets
• add html/css support to Godot UI widgets
• e.t.c.

You can create them in two ways:

• Complex way: see cobalt/render_tree/skottie_node.h
• Better and easier way: see src/cobalt/src/cobalt/render_tree/custom_node.h and src/extended_html/input_box/input_node.h

Just wrap your GUI element into html node and bind cobalt event to your GUI event.

You may also need to convert your GUI element into pixels, so it will be possible to use it as SKIA texture. For very complex UI you may want to create one big texture instead of a lot of smaller ones (for performance reasons).

Your GUI system will gain not only ease of designing via html/css, but also css animation system, 3D on-hover effects, e.t.c.

Related to #2