Auto generate dark mode previews and screenshots (#776)

With this change, composable previews and screenshots should be created with just:
```
@ElementPreviews
@Composable
fun MyViewPreview() {
    ElementPreview { 
        MyView()
    }
}
```

- Adds `@ElementPreviews` which is a shorthand for:
```
@Preview(name = "D")
@Preview(name = "N", uiMode = Configuration.UI_MODE_NIGHT_YES)
```
Should be used in connection with the now public `fun ElementPreview()` composable.

- Adds ElementPreviews to previewAnnotations in dangerfile
- Screenshots of night mode previews are now rendered with night mode
- Replaces `ElementPreviewLight` and `ElementThemedPreview` with `ElementPreview`
- Deprecates `ElementPreviewDark` which should be removed.
- Remaining usages of `ElementPreviewDark` are now ignored during screenshot tests

appnav/src/main/kotlin/io/element/android/appnav/loggedin/LoggedInView.kt

@@ -20,11 +20,11 @@ import android.app.Activity
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.platform.LocalContext
-import androidx.compose.ui.tooling.preview.Preview
+import io.element.android.libraries.designsystem.preview.ElementPreviews
 import androidx.compose.ui.tooling.preview.PreviewParameter
 import io.element.android.libraries.androidutils.system.openAppSettingsPage
+import io.element.android.libraries.designsystem.preview.ElementPreview
 import io.element.android.libraries.designsystem.preview.ElementPreviewDark
-import io.element.android.libraries.designsystem.preview.ElementPreviewLight
 import io.element.android.libraries.permissions.api.PermissionsView
 
 @Composable
@@ -43,12 +43,13 @@ fun LoggedInView(
     )
 }
 
-@Preview
+@ElementPreviews
 @Composable
-fun LoggedInViewLightPreview(@PreviewParameter(LoggedInStateProvider::class) state: LoggedInState) =
-    ElementPreviewLight { ContentToPreview(state) }
+fun LoggedInViewLightPreview(@PreviewParameter(LoggedInStateProvider::class) state: LoggedInState) {
+    ElementPreview { ContentToPreview(state) }
+}
 
-@Preview
+@ElementPreviews
 @Composable
 fun LoggedInViewDarkPreview(@PreviewParameter(LoggedInStateProvider::class) state: LoggedInState) =
     ElementPreviewDark { ContentToPreview(state) }

appnav/src/main/kotlin/io/element/android/appnav/root/RootView.kt

@@ -22,14 +22,14 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.runtime.Composable
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
-import androidx.compose.ui.tooling.preview.Preview
+import io.element.android.libraries.designsystem.preview.ElementPreviews
 import androidx.compose.ui.tooling.preview.PreviewParameter
 import io.element.android.features.rageshake.api.crash.CrashDetectionEvents
 import io.element.android.features.rageshake.api.crash.CrashDetectionView
 import io.element.android.features.rageshake.api.detection.RageshakeDetectionEvents
 import io.element.android.features.rageshake.api.detection.RageshakeDetectionView
+import io.element.android.libraries.designsystem.preview.ElementPreview
 import io.element.android.libraries.designsystem.preview.ElementPreviewDark
-import io.element.android.libraries.designsystem.preview.ElementPreviewLight
 import io.element.android.libraries.designsystem.theme.components.Text
 import io.element.android.services.apperror.impl.AppErrorView
 
@@ -67,11 +67,13 @@ fun RootView(
     }
 }
 
-@Preview
+@ElementPreviews
 @Composable
-internal fun RootLightPreview(@PreviewParameter(RootStateProvider::class) rootState: RootState) = ElementPreviewLight { ContentToPreview(rootState) }
+internal fun RootLightPreview(@PreviewParameter(RootStateProvider::class) rootState: RootState) {
+    ElementPreview { ContentToPreview(rootState) }
+}
 
-@Preview
+@ElementPreviews
 @Composable
 internal fun RootDarkPreview(@PreviewParameter(RootStateProvider::class) rootState: RootState) = ElementPreviewDark { ContentToPreview(rootState) }