fix: emitFile, eager/priority modes, noscript, srcset

[lxsmnsyc]

Summary

Stops the browser from ever downloading the untouched original, sends processed
files through the bundler, and adds an eager prop for the image above the
fold. Readers with no JavaScript now get the image.

Changes

• The img carries a srcset built from the last output format. A browser that
  supports none of the source types now picks a sized variant instead of the
  full size original.
• The order of the output option now matters. The last format is the fallback,
  so it should be the most widely supported one.
• The source module points at the largest variant of the fallback format. The
  original file is no longer imported, so it never reaches the bundle.
• Processed files go through the bundler on build with emitFile, so base,
  assetsDir and the build manifest apply to them. The dev server still writes
  them to the public directory.
• SolidImage takes an eager prop. The image loads without waiting for the
  observer, and the server renders it in full so the browser finds it while it
  parses the page.
• The server renders a noscript copy of the image. Browsers never load the
  content of a noscript element, so it costs nothing for everyone else.
• Variant groups are computed once in a memo and shared by the source elements
  and the img.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/@solidjs/image@5

commit: 3659561