Add Asset title text outline

[hankjordan]

Closes #1951

[rparrett]

I think we should figure out why the 50% opacity black background for the title div is not working in some environments.

[doup]

I think that this PR should be considered on its own as a way to improve assets legibility (I personally don't think it's necessary, but maybe other people think otherwise) not as a solution for #1951. #1951 has a wider impact than the issue we've noticed in the assets and the correct solution is #1953.

[doup]

In general, colors shouldn't be used directly, define a --asset-cart-title-text-shadow-color (verbose… 🤮) in _vars.scss in its corresponding section. The reason is that this will allow to change the shadow color for light mode.

@rparrett FYI, in case you see a similar issue in other PRs.

[doup]

Anyway, no need to do the change unless we agree that we want the text shadow.