This commit replaces the `XhrHttpBackend` with the `FetchBackend` as the default implementation of the `HttpBackend`.
This introduces a breaking change a the `FetchBackend` does not support the report progress for uploads.
The previous behavior (`HttpXhrBackend`) can be restored by setting `withXhr()` in the `provideHttpClient()` provider function.
DEPRECATED: `withFetch` is now deprecated, it can be safely removed.
BREAKING CHANGE: Use the `HttpXhrBackend` with `provideHttpClient(withXhr)` if you want to keep supporting upload progress reports.