[mathml-core] Enabling MathML-Core

As discussed in the core meeting, the browser doing the most active
development against the spec is the new implementation being upstreamed
right now. If you would like to test or run tests in order to understand,
experiment, open issues, etc - you can do this in any chromium-based
browser (Chrome, Chromium, Edge, Brave, Samsung Internet, etc), all you
have to do is enable experimental web platform features. Here's an article
about how to do that.

https://www.wpxbox.com/edge-how-to-enable-experimental-features/

Note you don't need any special download version, but they don't all
necessarily update in sync or at the same schedule so there will be cases,
for example, where it might make sense to get a different (Canary) build
and set this feature on that instead.  Note that once you turn it on, it
will be on until you turn it off again which can sometimes be misleading if
you're looking into the question of "what is shipping _not_ behind a flag",
so getting a different build for this purpose is pretty handy at keeping
them straight - if that is something that would bug you.


-- 
Brian Kardell :: @briankardell :: bkardell.com