argdown-map.js loads once for each argument map on the page

[DawnPaladin]

argdown-map.js (a needed file for web components) is loaded once for each argument map on the page. This causes the error "Uncaught DOMException: CustomElementRegistry.define: 'argdown-map' has already been defined as a custom element" to appear in the developer console. To improve performance and clear the error, it should be loaded only once.