[WIP] Skip some client tests for SSR

[PaulBGD]

This adds the skip-ssr option for tests. This builds on top of #253

There are a few tests that I think should pass and are issues with the SSR:

• component-binding
• component-binding-nested
• raw-mustaches
• component-yield
• svg-xmlns (waiting on xmlns should be added as an attribute for consistency #262)
• text-node-top-level

[PaulBGD]

@Rich-Harris Each of the tests that are currently failing appear to be issues with the SSR. Should I create an issue for each one of these then?

For example component-binding fails because the parent component doesn't take the default 2 way binded value from the child component, so x is undefined instead of 0.

[Conduitry]

raw-mustaches doesn't look like a necessarily valid failure to me. On the client side, raw mustaches are handled by creating empty <noscript> elements, and then inserting the HTML adjacent to them. The server-side code doesn't need to do this. I don't think we need to enforce parity here.

[PaulBGD]

@Conduitry The server should render the same code for rehydration purposes.

[Rich-Harris]

Re raw-mustaches and <noscript> — I think it's okay if the SSR'd HTML doesn't include it, since any rehydration process will presumably need to be able to handle missing elements somehow anyway (still not entirely sure how rehydration will work though).

Also, there are definitely times when you might want to SSR parts of your app and then only instantiate parts of it on the client (we're doing exactly that in one of our current projects — all the workflow and performance benefits, but very little duplicated content), and in those cases skipping <noscript> is definitely valid