feat: html and vue embedding

Prints srcset, iframe allow, class, style, event handler, and Vue
directive values as Prettier does, with the code going to the Embed
hook under Prettier's parser names. Drops bun's corrections where
they move Prettier's own fixtures: hidden blocks kept inline, SVG text
edges, and ASCII-only class name splitting. Whitespace-only input
prints nothing, as in Prettier's core.

Conformance: html 237/245, vue 155/194.