No scrollbars, things mostly working

[andrewsavage1]

Bug: 435264179

[github-actions]

🤖 Gemini Suggested Commit Message

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cobalt: Hide scrollbars by default

Add the kHideScrollbars switch to the Cobalt toggle switches list. This
ensures that scrollbars are suppressed by default across Starboard
platforms to align with the intended user interface design.

Bug: 435264179

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