[selected-network-controller] Proxy all domains, even those without permissions

[Gudahtt]

The SelectedNetworkController currently constructs a proxy for any domain that has permissions. Other domains have no associated proxy, so the getProviderAndBlockTracker method would throw an error.

This is problematic because we grab the network client for an origin a single time when constructing an RPC pipeline for that origin in the MetaMask extension. We don't re-create the RPC pipeline when permissions change. That means that the pipeline is setup with the wrong network client (see here for more details on this bug: MetaMask/metamask-extension#23509 )

To resolve this problem, we can instead keep network client proxies for all origins, not just those with permissions. Origins without permissions still should not have a selected network client ID state, but they can have proxies that point at the globally selected network client. That way, when the origin is granted permissions, we can redirect this proxy to the selected network client and everything works smoothly, without needing to reconstruct the RPC pipeline.

Note that this would result in a memory leak, as we'd be creating a proxy for every single origin visited by the user. We can counteract this by storing the proxies as WeakRefs using the strategy described here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Memory_management#weakrefs_and_finalizationregistry

[Gudahtt]

This is only partially fixed, we need #6063 to be merged as well before this can be closed