Add `outlineWidth` to `Cue`

[LagradOst]

Fixes #1834, by adding an extra field to Cue to inform the painter about the outline width of the subtitle.

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[LagradOst]

This is not ready for review yet, due to the confusing painting in updateWebView that I am unsure how to update. @icbaker could you clarify how to add Cue specific outlines when convertCaptionStyleToCssTextShadow is only called once per list of cues. I dont see a way to make it cue specific in a clean way.

[LagradOst]

@icbaker I believe I added everything needed for text outline using a span. However I an unable to test the webview text, so I added what I think will work.

[KingLucius]

@icbaker any update about that PR?

[icbaker]

However I an unable to test the webview text, so I added what I think will work.

Why is this? You should be able to enable it in any app using PlayerView (including our demo):

playerView.getSubtitleView().setViewType(SubtitleView.VIEW_TYPE_WEB);