Esm host bundling

[dannyleech]

Fixes ESM host builds failing on map engines they don't use (e.g. Can't resolve 'ol/...' when using /plugins/draw with MapLibre).

• maplibre-gl stays a dependency; ol, proj4 and @arcgis/core are optional peers. All engines are external in ESM builds, so hosts share one copy (datasets' OpenLayers adapter: 437 KB → 16.5 KB).
• Datasets and draw adapter chunks no longer load another provider's adapter (OpenLayers maps were downloading the MapLibre draw adapter).
• UMD builds no longer bundle Esri code (datasets UMD: 105 MB → 584 KB).
• New "Bundler configuration (ESM)" docs for ignoring unused engines; datasets and draw link to it.

Tested using Claude with ESM (webpack, Vite, Rollup, esbuild) and UMD with MapLibre and OpenLayers, with and without datasets and draw.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud