test: split hot module reload HMR test into multiple files (#79067)
Split long-running hot module reload hmr test to parallelize and reduce
CI time.
Port of https://github.com/vercel/next.js/pull/73620, confirmed no new
changes.
x-ref:
https://github.com/vercel/next.js/commits/canary/test/development/basic/hmr/hot-module-reload.test.ts