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

features/networkmonitor/api/src/main/kotlin/io/element/android/features/networkmonitor/api/ui/ConnectivityIndicatorView.kt

@@ -43,11 +43,11 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.ColorFilter
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.font.FontWeight
-import androidx.compose.ui.tooling.preview.Preview
+import io.element.android.libraries.designsystem.preview.ElementPreviews
 import androidx.compose.ui.unit.dp
 import io.element.android.libraries.designsystem.ElementTextStyles
+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.ui.strings.CommonStrings
 
 @Composable
@@ -109,15 +109,15 @@ private fun StatusBarPaddingSpacer(modifier: Modifier = Modifier) {
     Spacer(modifier = modifier.statusBarsPadding())
 }
 
-@Preview
+@ElementPreviews
 @Composable
 internal fun PreviewLightConnectivityIndicatorView() {
-    ElementPreviewLight {
+    ElementPreview {
         ConnectivityIndicatorView(isOnline = false)
     }
 }
 
-@Preview
+@ElementPreviews
 @Composable
 internal fun PreviewDarkConnectivityIndicatorView() {
     ElementPreviewDark {