Support dynamic values in `local-class`

[dfreeman]

Currently the preprocessor will reject non-static local-class values, e.g.

{{my-component local-class=(some-kind-of subExpression)}}

There's no technical reason we can't handle this case, but it does raise a couple of interesting questions. The simplest translation of the above would look something like:

{{my-component class=(get styles (some-kind-of subExpression))}}

However, this wouldn't handle cases like this (contrived) example where multiple class names are produced:

{{my-component local-class=(concat 'foo bar')}}

For these cases, we'll probably need to introduce a helper to split the string and look up the appropriate classes, so the compiled version might look something like:

{{my-component class=(lookup-module-styles (unbound styles) (some-kind-of subExpression))}}

[dfreeman]

Fixed by #40. A new release is on the way by the end of this week, pending an update for #22 and some additional Glimmer 2 fallout in the AST transform that was uncovered by this change.