Add an AccountProvider type and use it within the authentication flow. (#6103)

* Add an AccountProvider type and use it within AppSettings.

* Use the AccountProvider type within the Authentication flow too.

* Fix unit test compilation with Swift 6.4

* Make sure defaultAccountProvider takes allowOtherAccountProviders into account.

* Document a caveat on using AuthenticationService.homeserver.value.accountProvider.

ElementX/Sources/Application/Settings/AppSettings.swift

@@ -78,7 +78,7 @@ final nonisolated class AppSettings: @unchecked Sendable {
     // MARK: - Hooks
     
     // swiftlint:disable:next function_parameter_count
-    func override(accountProviders: [String],
+    func override(accountProviders: [AccountProvider],
                   allowOtherAccountProviders: Bool,
                   hideBrandChrome: Bool,
                   pushGatewayBaseURL: URL,
@@ -143,7 +143,7 @@ final nonisolated class AppSettings: @unchecked Sendable {
     ///
     /// Account provider is the friendly term for the server name. It should not contain an `https` prefix and should
     /// match the last part of the user ID. For example `example.com` and not `https://matrix.example.com`.
-    private(set) var accountProviders = ["matrix.org"]
+    private(set) var accountProviders: [AccountProvider] = [.managed(serverName: "matrix.org", baseURL: "https://matrix-client.matrix.org")]
     /// Whether or not the user is allowed to manually enter their own account provider or must select from one of `defaultAccountProviders`.
     private(set) var allowOtherAccountProviders = true
     /// Whether the components surrounding the app brand/logo should be hidden or not
@@ -188,8 +188,12 @@ final nonisolated class AppSettings: @unchecked Sendable {
     @UserPreference(key: "previousServers", defaultValue: [])
     var previousServers: [String]
     
-    var defaultServer: String {
-        previousServers.first ?? accountProviders[0]
+    var defaultAccountProvider: AccountProvider {
+        if allowOtherAccountProviders {
+            previousServers.first.map { .generic($0) } ?? accountProviders[0]
+        } else {
+            accountProviders[0]
+        }
     }
     
     // MARK: - Security