* Rename `provider` to `providerConfig`
The network controller `provider` state has been renamed to
`providerConfig`. This better reflects what this state is, and makes
this controller more closely aligned with the core network controller.
All references to the provider configuration have been updated to
prefer `providerConfig` over `provider`, to make the distinction clear
between a provider and provider config.
Closes#18902
* Add migration
The `getProviderConfig` selector is now used anywhere the `provider`
state was previously referenced directly. This was done to simplify
renaming this state from `provider` to `providerConfig` in a later PR.
Note that there are many opportunities left to use more-specific
selectors (e.g. `getChainId()` over `getProviderConfig().chainId`), but
that was intentionally omitted from this PR to reduce the size. I
started going down this path and it quickly exploded in scope.
Relates to #18902
