perf: Define top-level earcut worker pool (#954)

### Change list

- Define an earcut worker pool once in global scope, and reuse it for
any polygon layers
- This should (significantly?) improve perf for any polygonal layers
(though not the h3 layer)
- Load the worker source as _text_ from the version in `node_modules`.
(`earcut.worker.min.js` is 15KB, and much easier to not have it be
async). This means we don't need any async step, nor do we need to keep
the worker source version in sync with our `geoarrow-js` version in
`package.json`

Depends on geoarrow/geoarrow-js#39

Closes #909

Author: kylebarron

build.mjs

@@ -1,10 +1,10 @@
-import esbuild from "esbuild";
+import autoprefixer from "autoprefixer";
 import dotenv from "dotenv";
+import esbuild from "esbuild";
 import { sassPlugin } from "esbuild-sass-plugin";
-import tailwindcss from "tailwindcss";
-import autoprefixer from "autoprefixer";
 import postcss from "postcss";
 import postcssPresetEnv from "postcss-preset-env";
+import tailwindcss from "tailwindcss";
 
 // Load environment variables from .env file
 dotenv.config();
@@ -40,6 +40,10 @@ esbuild.build({
       },
     }),
   ],
+  loader: {
+    ".worker.js": "text",
+    ".worker.min.js": "text",
+  },
   // Code splitting didn't work initially because it tried to load from a local
   // relative path ./chunk.js
   // splitting: true,