feat(compiler): remove whitespace from static class attributes

[royeden]

See issue #4251

Fixes compiled whitespace in static class attributes being preserved:

This repro compiles the following

<div class="
  asdf  
">Hello World!</div>

into

_createElementBlock("div", { class: "\n  asdf  \n" }, "Hello World!")

preserving whitespace after parsing.

This PR fixes that and normalizes whitespace in the DOM in case it's added via :class or :style binding.

• Related issue in Vue 2 and the PR with the fix for that version.
• Related issue in prettier.

Close #4251

[yyx990803]

After taking another look, I believe the runtime changes are not necessary when the compiler already outputs condensed class names, so I refactored to remove unnecessary abstractions.