Dark Mode support for Android ViewArticleActivity

(crossposting from the Zendesk Platform Developers Slack)

Hey team! - I wanted to ask about the ViewArticleActivity class in the Android SDK and a proposed change I have for the way that help_center_article_style.css is loaded. To be able to style ViewArticleActivity for Dark Mode, we would like to provide the CSS file based on our app's current mode. 

Unfortunately, while Android supports having things like drawable/ and drawable-night/ asset folders that are automatically swapped based on UI mode, this is not supported from the assets/ folder that the CSS_FILE constant is referencing. 

This means that it is impossible as of now to style the help articles with a Dark Theme because the CSS must be one, universal file. 

We are also unable to write to file:///android_asset at runtime, so a File I/O based solution would not work.

If we could provide either a replacement for the CSS_FILE constant to be able to point at our own .css file location when loading help articles or if the implementation could be changed to possibly check for UI mode and swap between a help_center_article_style.css and help_center_article_style_night.css file, that would be great. I think that the first suggestion would require less changes. 

Please let me know if I can provide any additional information!