Support "math" IA2 object attribute in Chrome and Firefox

[aleventhal]

Currently NVDA supports math on ROLE_SYSTEM_EQUATION objects by using ISimpleDOMNode::get_innerHtml().
In the interests of eventually being able to deprecate and remove ISimpleDOMNode support, NVDA should first check whether the "math" object attribute exists, and only use ISimpleDOMNode as a fallback.
Chromium has added support for this in recent Canary builds.
Here's a issue entry for this to also be supported by Mozilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1924832

[aleventhal]

AAM mappings issue: w3c/aria#2355

[NSoiffer]

Is this related to NVDA cannot navigate math content in Chromium ?

[aleventhal]

It didn't cause the problem, but the change that caused the problem is under the same project -- eventually getting rid of ISimpleDOMNode.

[Adriani90]

This is related or even a duplicate of #13702.