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

libraries/permissions/api/src/main/kotlin/io/element/android/libraries/permissions/api/PermissionsView.kt

@@ -18,11 +18,11 @@ package io.element.android.libraries.permissions.api
 
 import androidx.compose.runtime.Composable
 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.libraries.designsystem.components.dialogs.ConfirmationDialog
+import io.element.android.libraries.designsystem.preview.ElementPreview
 import io.element.android.libraries.designsystem.preview.ElementPreviewDark
-import io.element.android.libraries.designsystem.preview.ElementPreviewLight
 
 @Composable
 fun PermissionsView(
@@ -81,12 +81,13 @@ fun PermissionsView(
     }
 }
 
-@Preview
+@ElementPreviews
 @Composable
-fun PermissionsViewLightPreview(@PreviewParameter(PermissionsViewStateProvider::class) state: PermissionsState) =
-    ElementPreviewLight { ContentToPreview(state) }
+fun PermissionsViewLightPreview(@PreviewParameter(PermissionsViewStateProvider::class) state: PermissionsState) {
+    ElementPreview { ContentToPreview(state) }
+}
 
-@Preview
+@ElementPreviews
 @Composable
 fun PermissionsViewDarkPreview(@PreviewParameter(PermissionsViewStateProvider::class) state: PermissionsState) =
     ElementPreviewDark { ContentToPreview(state) }