test: break down metadata test suite into smaller ones (#67018)
### What
app-dir `metadata.test.ts` is pretty big and includes a lot of erroring
tests and navigation tests. Breaking them into smaller suites to avoid
the erroring on effect on others.
- metadata
- metadata-navigation
- metadata-thrown
Moved the metadata testing utils into `next-test-utils` for sharing
purpose.
Moved the hmr test to the bottom to avoid flakyness.
