Pluggable, lazily-imported map-link renderers by MIME type #1065

Currently in MapML.js, there's a mechanism to render pmtiles or mvt files via a "stylesheet module". i.e. markup like this

<map-link rel="stylesheet" type="application/pmtiles+stylesheet" href="lightTheme.js"></map-link>
...
<map-link rel="tile" type="application/pmtiles" tref="spearfish.pmtiles?theme=light"></map-link>

It would be great to be able to re-use this mechanism to create and dispatch custom rendering for idiosyncratic content types without bloating the core library via such dynamic imports, for example to custom render geotiff data:

<!-- geotiff-renderer.js is not part of the core -->
<map-link rel="stylesheet" type="application/geotiff+renderer" href="./geotiff-renderer.js"></map-link>
<map-link rel="tile" type="image/tiff; application=geotiff" tref="…"></map-link>

In light of the above the "+stylesheet" media type suffix might be incorrect, tbd, as it's a dynamic JavaScript module import internally.