use ConstantEvaluator for primitive values

[sigmundch]

When inlining the const constructor of an initializer annotation, we could use ConstantEvaluator to determine if the value is a simple primitive, if so, just write the primitive value (since they are cannonicalized).

This will allow us to support @HtmlImport in more cases, since we need to extract the string argument from it.

[jakemac53]

In the new plugin architecture which is coming, this won't be an issue. Plugins will have access to the fully resolved AST and can do this on their own as needed.