perf(ext/node): convert node:assert to lazy-loaded
Move the node:assert implementation into assert.ts (lazy_loaded_js
IIFE). Add assert_esm.ts as the thin ESM wrapper in lazy_loaded_esm.
Move node:assert/strict to lazy_loaded_esm as well.
Replace all `import ... from "node:assert"` in ext/node with
core.loadExtScript("ext:deno_node/assert.ts").
