feat(bazel): support spec bundling with rules_js

This is an initial, and still sufficient version of spec bundling for
`rules_js`. Notably it's significantly shorter and very clean. Very
convincing to see this short code snippet for a previously rather
complicated piece.

We will continue to need spec bundling for ESM Karma tests. This is
expected and even speeds up tests significantly, and improves stability.

Author: devversion

bazel/package.json

@@ -3,7 +3,8 @@
   "dependencies": {
     "@microsoft/api-extractor": "7.51.0",
     "typescript": "5.7.3",
-    "@types/node": "22.13.5"
+    "@types/node": "22.13.5",
+    "esbuild": "0.25.0"
   },
   "pnpm": {
     "onlyBuiltDependencies": []