Update MathJax contextual menus for assistive tools

[dpvc]

This PR implements the new menu structure that we discussed over the last few developer meetings.

While updating the menus, we also normalize how the settings are handled, so that the enableSpeech, enableBraille, enableEnrichment and enableExplorer document options control whether those actions are taken, and are controlled automatically by the menu settings. When enrichment is enabled, the accessibility submenus are made active (and the enable... options are set to true). This allows the explorer to run, and whatever settings are present in the Speech, Braille, and Explorer menus to take effect. Those submenus control the a11y settings of the document's options (and the menuOptions.settings section, which is what initializes the a11y values when the menu code is loaded, and are what are stored in the menu's localStorage cache).

All of this means that, for example, for speech to be added, both the document's enableSpeech and a11y.speech options must be true, and for the subtitles to be shown, the a11y.substitles option must also be true. Similarly for the Braille settings. This generated the changes to KeyExplorer.ts for example.

The setA11yOptions() function in explorer.ts is simplified by moving the handling of locale to the setA11yOption() function where all the other special keys are processed.

The ExplorerPool.ts file is modified to attach explorers when speech isn't enabled but one of Braille or magnification is (there were not separate explorer keys for these, as the speech explorer handles all three).

In semantic-enrich.ts, we add code to remove enrichment if the state drops below the enrichment state, and we add an error function to process enrichment errors that can be overriden by the user.

The MJContextMenu is modified to:

• Add a Braille Code item to the Show As and Copy to Clipboard submenus (enabled when Braille generation is active).
• Modify the DynamicSubmenus code to allow enabling of a non-empty menu to be controlled by a menu setting (so that, for example, the language submenu does not get enabled when speech is not being generated).
• The findID() method has been rewritten to not use find(), which descends into submenus too soon for findID().

The SpeechMenu.ts file uses the new DynamicSubmenus parameter to handle the language and clearspeak submenus.

The MenuHandler adds the enableSpeech and enableBraille options, and handles the transfer of the menu settings to the various enable... options. Note that enableExplorer and enableEnrichment are initially the same, since enrichment is all that is needed for the explorer at this point.

Finally, the Menu.ts file has significant changes to implement the new menu structure and loading of the needed components when the settings change. The explorer menu setting has been removed, since there is no longer an explicit menu setting for it (instead, it is controlled by enrichment setting).

It may be useful to turn off white-space difference when looking at the changes.

Note that you will need to use the lab-menu-update branch in the MathJax-dev repository to get the needed changes to the lab in order for the lab to work with this branch.

[dpvc]

I've made the name change to the Semantic Enrichment menu item.

I also made changes to some of the component config.json files to update them to handle the current interdependencies better. E.g., the explorer component no longer relies on ui/menu, so that has been removed from its config.json file and from the dependencies.js file, and since uses the a11y/speech/SpeechUtil.ts file and so does semantic-enrich, this is now shared between them rather than both including separate copies of it.

I've looked at the conflicts with the updates to the fix/ff_safari_issues branch, and there are four to be dealt with.

• In explorer.ts, I think you can remove the new lines that set the enable options, as these are handled by the menu (when you check or uncheck Generate in the Speech submenu, enableSpeech is set or unset (so enableSpeech tracks options.a11y.speech automatically. Similarly for Braille. Note that since these lines are in the explorable() function, and that runs after the attachSpeech() function, setting these options here is too late anyway. If you want to have the a11y options for the enable options, it might be best to do that in the constructor rather than in explorable().

• In ExplorerPool.ts, I had handled the speech/braille/keyMagnifier issues by modifying line 239 in the conflict editor. You can decide which method to use, but note that I made an a11y variable at line 220 of the conflict editor, and that is used later, so you should keep that line. My lines 221 and 222 should be replaced by your line 224, though. If you keep your changes, you can use a11y in line 231 to simplify that (and probably move it onto the previous line). And of course you would remove my changes from line 239.

• In KeyExplorer.ts, I think you want to keep my lines, for when the menu isn't being used.

• In semantic-enrich.ts, my changes are equivalent to yours, but I have set up an options variable earlier that I use here, where you use the full path to the options.

So I think there is not much problem with the conflicts, and they are easily sorted out.