Add real values for all MathML features

[Elchi3]

The first two commits indicate no MathML support at all in Edge or Edge Mobile
See https://developer.microsoft.com/en-us/microsoft-edge/platform/status/mathml/

The third commit also updates the few Firefox and Safari values with real values.

With this PR, 100% of the data in the mathml/ folder has real values for the 8 tracked browsers.

Overall, it changes the stats a bit as well:

Before (current master):

browser	real values	true values	null values
total	55.26%	22.23%	22.51%
edge	53.23%	20.25%	26.53%

After this PR:

browser	real values	true values	null values
total	55.49%	22.20%	22.32%
edge	54.83%	20.25%	24.93%

[ExE-Boss]

If it’s not supported on Desktop, then it’s definitely not supported on Mobile.

[Elchi3]

Thanks @ExE-Boss, I've updated the PR.

[Elchi3]

Maybe @fred-wang can help reviewing or knows someone who could.
(the Safari and Firefox changes which are in the 3rd commit).

[fred-wang]

IIUC Microsoft Edge uses different web engines on mobile (e.g. blink on android and webkit on iOS). Also Microsoft plans to switch to blink on Windows too, so that would mean the same result as Chrome ( https://blogs.windows.com/windowsexperience/2018/12/06/microsoft-edge-making-the-web-better-through-more-open-source-collaboration/ ).

I don't know the exact versions for firefox/safari. I guess it is fine to put these values and fix them later if people report errors...

[ExE-Boss]

Except that edge_mobile refers to Microsoft Edge on Windows 10 Mobile, which stopped being updated with EdgeHTML 15.

[Elchi3]

Thanks @ExE-Boss and @fred-wang, let's merge this then.