Fix fetch cache key inputs and encoding (#46392
This ensures we properly filter caching on uncachable request methods by
default and correct encoding handling in edge runtime.
Fixes: https://github.com/vercel/next.js/issues/46349
x-ref: [slack
thread](https://vercel.slack.com/archives/C042LHPJ1NX/p1677253242022489)
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)
