`<mspace linebreak="newline" />` not working with explorer accessibility.

Created by: henok-tesfaye

Issue Summary

When the accessibility explorer is activated, MathML line break, <mspace linebreak="newline" />, won't work.

Steps to Reproduce:

1. Open https://jsbin.com/sajujukiwe/1/edit?html,js,output
2. Check how math expression is displayed by making accessibility explorer property to false and true.

When explorer is set to false there will be a line break which is what I want but I also want the accessibility feature.

Technical details:

• MathJax Version: 2.7.7
• Client OS: Mac OS X 10.14.6
• Browser: Chrome Version 84.0.4147.105 (Official Build) (64-bit)

Supporting information:

https://jsbin.com/sajujukiwe/1/edit?html,js,output