Optional day night preview annotation (#793)

Adds the `@DayNightPreviews` annotation that when used on a composable will:
- Display both a day mode and night mode preview in Android Studio.
- Produce both a day and night screenshot during screenshot testing.

The usage of this new annotation is optional, all the current previews continue to work without breakages.
New code can use, when appropriate, the new `@DayNightPreviews` annotation and replace the pattern using three `LightPreview/DarkPreview/ContentToPreview` functions with:

```
@DayNightPreviews
@Composable
fun MyScreenPreview(@PreviewParameter(MyStateProvider::class) state: MyState) {
    ElementPreview {
        MyScreen(
            state = state,
        )
    }
}
```

tools/danger/dangerfile.js

@@ -132,7 +132,8 @@ if (allowList.includes(user)) {
 
 const previewAnnotations = [
     'androidx.compose.ui.tooling.preview.Preview',
-    'io.element.android.libraries.designsystem.preview.LargeHeightPreview'
+    'io.element.android.libraries.designsystem.preview.LargeHeightPreview',
+    'io.element.android.libraries.designsystem.preview.DayNightPreviews'
 ]
 
 const filesWithPreviews = editedFiles.filter(file => file.endsWith(".kt")).filter(file => {