Add config option to disable the Explorer's Help dialog and info icon.

[icc]

Is your feature request related to a problem? Please describe.
The new Explorer is great, but it introduce a tall UI element that sets requirements to the height of the page. This can be problematic in usecases where the content with math is displayed in iframes with limited height, this means that the Help Dialog is way to large to display. For now our workaround is to fork MathJax to disable the help dialog and display the information elsewhere.

Describe the solution you'd like
It would be great if this was a simple config instead, similar to how you can disable the menu.

Describe alternatives you've considered
An optional way of solving this could be to have an event when the dialog opens or closes where the devs can add code to adapt the size of the iframe so that the help dialog is visible.

[icc]

For refrence, here is the code we're using to disable it: https://github.com/mathjax/MathJax-src/compare/master...h5p:MathJax-src:add-option-to-disable-help-dialog?expand=1

[dpvc]

OK, I don't really like not providing help for users of assistive technology, but I don't really like disabling the menu either, and there is an option for that. I understand your situation.

I have made a PR for it, though it is not quite the same as yours. For one, the option is enableExplorerHelp, since enableHelp is not specific enough (it could have referred to the MathJax help item in the main menu, for example).

It also makes sure the h key passes through when not being used for help, and that the "press H for help" message isn't spoken even if the menu option for it is checked.

Finally, it sets the option in the ts/a11y/explorer.ts code as well, since the menu might not be loaded but the explorer is.

Related issue: #3409