Configure the AuthenticationService later now that we have 2 flows on the start screen. (#3316)

* Don't query the homeserver until confirming it (or selecting a different one).

* Setup the infrastructure to test AuthenticationService.

Implement basic tests for configuration & password login.

* Use the real AuthenticationService with a mock Client in all of the tests.

* Add tests for the ServerConfirmationScreenViewModel.

* Remove redundant view state and test for it.

ElementX/Sources/Mocks/AuthenticationClientBuilderFactoryMock.swift

@@ -0,0 +1,22 @@
+//
+// Copyright 2024 New Vector Ltd.
+//
+// SPDX-License-Identifier: AGPL-3.0-only
+// Please see LICENSE in the repository root for full details.
+//
+
+import Foundation
+import MatrixRustSDK
+
+extension AuthenticationClientBuilderFactoryMock {
+    struct Configuration {
+        var builderConfiguration: AuthenticationClientBuilderMock.Configuration = .init()
+    }
+    
+    convenience init(configuration: Configuration) {
+        self.init()
+        
+        let clientBuilder = AuthenticationClientBuilderMock(configuration: configuration.builderConfiguration)
+        makeBuilderSessionDirectoriesPassphraseClientSessionDelegateAppSettingsAppHooksReturnValue = clientBuilder
+    }
+}