Refine sign in flow to match designs and iOS flow (#100)

* Fix dark theme

* First attempt at replicating iOS' UI & flows.

* Try to fix Maestro tests

* Add error dialogs and tests

* Remove unused modifiers

* Try to fix detekt issues

* Tidy up maestro login flow a bit

* Add `CompoundColorPalette` with some needed colors

* Fixes to designs

* Fix detekt issues

* More design fixes

* Some other minor design fixes

* Add changelog

* Minor tweaks.

* Remove legacy dark material theme as it's no longer needed.

* Move sliding sync 'learn more' url to constants object

* Remove unused focusManager

* Change how the displayed homeserver works

* Keep user input as homeserver if it's valid

* Remove `CompoundColorPalette`, try to fix issue when toggling dark mode.

* Add `@Stable` to the theme, adjust how it toggles in dark mode

* Remove unused strings

* Update screenshots

* Re-organize components in LoginRootScreen

* Bump min coverage to 55, max to 60

* Always replace the snapshots contents when running `recordPaparazzi`

* Fix dark theme preview of components using content colors

* Add `BackButton` component

* Handle errors with dialogs in a generic way

* Align our Dialog components with the designs, use them were needed

* Use a `MatrixHomeserverDetails` data class instead of just an URL.

* `AuthenticationService.getHomeserverDetails()` now returns a `StateFlow`.

Also, try to fix coverage issues in tests.

samples/minimal/src/main/kotlin/io/element/android/samples/minimal/LoginScreen.kt

@@ -33,7 +33,8 @@ class LoginScreen(private val authenticationService: MatrixAuthenticationService
         val state = presenter.present()
         LoginRootScreen(
             state = state,
-            modifier = modifier
+            modifier = modifier,
+            onBackPressed = {},
         )
     }
 }