Copy __locales__ for all components, and improve default json loading.

[dpvc]

This PR adds copy blocks to the component configuration files for the TeX packages that have __locales__ files.

In addition, it fixes the component name for the main TeX __locales__ file : [tex] translates to [mathjax]/input/tex/extensions, which is where the webpacked versions go. The correct component name is 'input/tex'. In order to get this to work, the components/mjs/core/core.js file is modified to always use Package.resolvePath(), not just when the package name starts with [. We also add a mathjax.json specification in core.js so that it works in node applications (that use the components framework) without their having to override the MathJax.loader.json configuration value. We include it here so that the webpack comment is present, as this .js file doesn't get transpiled, which would remove comments. (Alternatively, it could be in ts/mathjax.ts, with a separate tsconfig file like the one used for the web worker, but I think this is easier.) The components tsconfig file is modified to not remove that comment when compiling the CJS versions.

The main input/tex config file copies both the input/tex/__locales__ directory and the input/tex/base/__locales__ directory, since the base package doesn't have a separate component to do the copying (though I suppose we could make a component directory for it with just a config file for copying the locales, if you thin that is cleaner).

The components/mjs/startup/init.js file is modified to load the core component, so that it will share the same Locale object as the core component. Without this, people use use <script src="https://cdn.jsdelivr.net/npm/mathjax@4/startup.js> and the loader.load array to load individual components would end up having a separate Locale object where the strings get registered, and when startup does Locale.setLocale(), it would be with its own copy, and there would be no registered packages.

The Bbox.test.ts doesn't need to specify async, as the setupTex() command already returns a promise.

Finally, there are new mjs/json.ts and cjs/json.ts files to implement the mathjax.json method that supports both browser and node use. Node users are supposed to load one of the asyncLoad implementations, but in case they don't this will allow the locales to be loaded anyway. Without that, the locale loading would break existing node applications that don't currently import one of the asyncLoad files. Because the CJS typescript settings don't currently allow import() to include {with: {type: 'json'}}, we use a separate mjs and cjs implementation, where the cjs version uses require() rather than import(), since that handles JSON files automatically.

[zorkow]

Lgtm. I've already added copy blocks to the config.json files yesterday (not yet pushed), so I might get some conflicts...