TB 44796: Convert `TorProviders` types to strings.

This allows them to be used in log messages.

TB 44796: Add `TorProviderState`, which tracks the state of a provider.

We create a new `TorProviderBase` class which tracks this state, and the
existing `TorProvider` now extends.

`TorProviderBuilder.sys.mjs`:
+ We provide a callback to let the current provider instance let
  `TorProviderBuilder` know when this state has changed.
+ This will emit `TorProviderSateChanged` as a replacement for
  `TorProcessExited`. The `Stopped` state has the same role as the
  previous event, except it is more generic. This event also lets any
  consumers know when a provider has been just replaced (`Starting`) and
  successfully initialised (`Running`).

`TorControlPort.sys.mjs`:
+ Add `onClosed` callback to signal to the `TorProvider` that the
  control port has closed, which will trigger `_stoppedInternal`.
+ Delay adding the event handler so the `TorProvider` only listens to a
  control port after it is successfully set up and adopted by the
  `TorProvider`.

`TorProvider.sys.mjs`:
+ `TorProvider` no longer emits `TorProviderTopics.ProcessExited`.
+ Instead, `TorProvider` calls `_stoppedInternal` whenever the provider
  stops running. I.e. whenever the control port is closed, which
  includes when the process exits but also other scenarios where the
  control port might close unexpectedly.

TB 44796: Convert the "none" provider into a `TorProviderNone` class, so
it can be handled by the same logic as `TorProvider`.

TB 44796: Add the `settledState` method to allow `TorConnect` to wait
for the first provider's state after it has settled. This is a way to
get the current providers state prior to having listened to
`TorProviderStateChange`.

Add the `replace` method to allow `TorConnect` to request a new provider
on the user's behalf.

TB 44796: Drop `#torExited` and internals of `firstWindowLoaded` and
instead use promptProviderState which handles both. These are only
temporary changes to be dropped in #43570.

TB 44796: Listen for ProviderStateChanged rather than ProcessStopped.

TB 44796: Drop `TorProvider.isRunning`.

TB 44796: Use `TorProvider.state` instead of `isRunning`.