Cleanup element call and UI (#4641)

* Use ElementTheme.colors.bgCanvasDefault instead of MaterialTheme.colorScheme.background

Even if the value is the same, we should use color from ElementTheme.

* Remove background management of ElementCallActivity. It does not work as expected and also changing theme during a call would require to load the url again with the new theme.

* Do not use isSystemInDarkTheme() directly.

* Use bgSubtleSecondary for background color of Preview.

* Use default colors for Preview.

* Fix copy paste issue.

* Update screenshots

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Co-authored-by: ElementBot <android@element.io>

features/preferences/impl/src/main/kotlin/io/element/android/features/preferences/impl/advanced/AdvancedSettingsView.kt

@@ -49,8 +49,8 @@ fun AdvancedSettingsView(
             title = stringResource(id = CommonStrings.common_appearance),
             selectedOption = state.theme,
             options = ThemeOption.entries.toPersistentList(),
-            onSelectOption = { logLevel ->
-                state.eventSink(AdvancedSettingsEvents.SetTheme(logLevel))
+            onSelectOption = { themeOption ->
+                state.eventSink(AdvancedSettingsEvents.SetTheme(themeOption))
             }
         )
         ListItem(