synthetic-to-native transform should handle SLDS utility classes

[nolanlawson]

One of the biggest blockers of moving from synthetic shadow to native shadow is HTML templates containing SLDS utility classes, e.g.:

<template>
  <h1 class="slds-text-heading_large">SLDS Example</h1>
  <div class="slds-p-top_medium">
    <p>Hello!</p>
  </div>
</template>

As part of synthetic-to-native, we could inject the minimal SLDS style rules into the component.css file, e.g.:

.slds-text-heading_large {
  font-size: 1.75rem;
  line-height: 1.25;
}

.slds-p-top_medium {
  padding-top: 1rem;
}

This would not work for all cases (namely selectors that cross shadow boundaries), but it could be a good ~95% solution with minimal perf impact (since it wouldn't include all of SLDS, just the minimal rules needed).

Another downside is that this would not keep pace with SLDS updates, but maybe this is okay since this is intended as a one-time operation. Perhaps another option here would be to transform from classes to styling hooks (i.e. CSS custom properties, which pierce native shadow roots).