Yield `isActive` in block template about dynamic-link

[asross]

Thanks for creating this issue, the feature idea sounds good to me! I’m on a vacation right now but I’ll try to take a pass at this soon. PRs are also welcome :)

As a workaround for anyone reading this before we implement this feature, you can always include both conditionals inside different elements, but use CSS to only show one (based on the active class). Another option is just to have a higher level conditional. But it definitely makes sense to be able to have conditionals inside the block :)

[lougreenwood]

I'm happy to attempt a PR, any pointer on how you might approach this? I was thinking it might be as simple as adding a template for the component and yielding isActive from there?