chore: Add type: "module" to package.json

This means that .js files will by default be interpreted as ESM
rather than CJS—which is correct, since almost all our source files
are in fact ES modules using import.

This allows removal of test/webdriverio/test/package.json, which
was preventing npm scripts (e.g. "npm test") from working properly
in that directory.

A few config files that do in fact use require() are renamed to
.cjs to ensure they are correctly interpreted.

Author: cpcallen

eslint.config.js renamed to eslint.config.cjs

@@ -21,6 +21,7 @@
     "wdio:clean": "cd test/webdriverio/test && rm -rf dist",
     "wdio:run": "npm run wdio:build && cd test/webdriverio/test && npx mocha dist"
   },
+  "type": "module",
   "main": "./dist/index.js",
   "module": "./src/index.js",
   "unpkg": "./dist/index.js",