Introduce "Black" theme and refactor theme handling

* Add `Theme.Black` to the `Theme` enum and update `isDark()` to include it.
* Refactor `ElementTheme` to accept a `Theme` object instead of a `darkTheme` boolean, allowing for more specific color mapping (e.g., setting `bgCanvasDefault` to `Color.Black` for the Black theme).
* Update `AdvancedSettingsPresenter` and `AdvancedSettingsState` to include "Black" as a user-selectable theme option.
* Adjust `ElementThemeApp` and `MaterialTextPreview` to handle the expanded theme selection.
* Add `ElementPreviewBlack` and update existing preview components to support the new theme.
* Update Konsist tests to ensure `@PreviewsDayNight` annotated functions don't have "BlackPreview" suffix.

tests/konsist/src/test/kotlin/io/element/android/tests/konsist/KonsistPreviewTest.kt

@@ -30,7 +30,8 @@ class KonsistPreviewTest {
             .assertTrue {
                 it.hasNameEndingWith("Preview") &&
                     it.hasNameEndingWith("LightPreview").not() &&
-                    it.hasNameEndingWith("DarkPreview").not()
+                    it.hasNameEndingWith("DarkPreview").not() &&
+                    it.hasNameEndingWith("BlackPreview").not()
             }
     }