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.

[icbaker]

This applies to the whole Cue

But for google/ExoPlayer#9391 I think we will need to be able to apply different outlining to different parts of text within a cue (in order to properly implement the TTML spec).

I think this points towards to using a custom styling span instead (google/ExoPlayer#9391 (comment)).

With a styling span, the answer to your WebView question then becomes to modify this class I think: https://github.com/androidx/media/blob/main/libraries/ui/src/main/java/androidx/media3/ui/SpannedToHtmlConverter.java

[LagradOst]

Bruh, that makes it a lot more complicated. However I assume that no extra paramater is needed in Cue then, as SpannableString is a CharSequence and outlinewidth can therefore piggyback from CharSequence text. That just makes the drawing a pita as we need to loop all spans.

Would something in the style of https://stackoverflow.com/questions/43275159/how-to-draw-a-spanned-string-with-canvas-drawtext-in-android work for SubtitlePainter? If so, what properties would this custom span have? Just outline width, or would I also need to support additional properties like color, or would that be a separate span that also would need support?

[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.