The version of rxjs used to build the repository has been updated to v7.
This required only minimal changes to the code. Most of which were type
related only due to more strict types in v7. The behavior in those cases
was left intact. The most common type related change was to handle the
possibility of `undefined` with `toPromise` which was always possible with
v6 but the types did not reflect the runtime behavior. The one change that
was not type related was to provide a parameter value to the `defaultIfEmpty`
operator. It no longer defaults to a value of `null` if no default is provided.
To provide the same behavior the value of `null` is now passed to the operator.
PR Close#53500
This commit introduces a new `HttpBackend` implentation which makes requests using the fetch API
This feature is a developer preview and is opt-in.
It is enabled by setting the providers with `provideHttpClient(withFetch())`.
NB: The fetch API is experimental on Node but available without flags from Node 18 onwards.
PR Close#50247
