This ensures we create any nested folders necessary when setting initial ISR cache entries with the filesystem cache. Also adds a regression test for this.
## Bug
- [x] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
Fixes: https://github.com/vercel/next.js/issues/38130
Continuation of https://github.com/vercel/next.js/pull/37258 this moves the LRU cache to the `file-system-cache` so that any different cache handlers don't need to disable the LRU cache as this may cause inconsistencies with some cache handlers that need to be the source of truth.
This refactors the `incremental-cache` and moves the file-system cache handling to it's own cache handler allowing it to be replaced by a custom cache handler (experimental).
Closes: https://github.com/vercel/next.js/pull/22619
## Bug
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `yarn lint`
- [ ] The examples guidelines are followed from [our contributing doc](https://github.com/vercel/next.js/blob/canary/contributing.md#adding-examples)
