v0.12.4: infrastructure, for real

I had to fix it again. Verdict: ES6 modules and automatic detection of node/browser environment doesn't work.

So now LaTeX.js (HtmlGenerator to be exact) simply assumes a DOM implementation, HtmlGenerator doesn't load svgdom itself anymore. Without support for top-level await in browsers, terser, and node, this just cannot be done properly in ES6.

Other changes:

• include LaTeXJSComponent in the main exports, don't create an extra bundle anymore
• include SyntaxError in the main exports
• to make sure that HtmlGenerator doesn't require a DOM implementation already on import anymore, it cannot create a cache of html elements directly; now create() takes a string or a factory function for element creation