Use Webview UI Toolkit for Visual Studio Code for webview controls

[daviddossett]

Proposal

Hi all! 👋

Now that we've released the Webview UI Toolkit for Visual Studio Code, I think it would great to swap the bespoke/styled UI components in the extension with their counterparts in the toolkit. This would reduce the load on maintainers to have to keep up with visual/theme/accessibility consistency with VS Code itself, among other advantages.

You can view the components in a Storybook environment here.

From what I've seen, the primary webviews in the extension use inputs, buttons (icon, primary, secondary), tags, checkboxes, and links. I believe the toolkit covers all of those components spare the split button currently used for selecting a merge method. That component is in our backlog to be added soon.

References

cc @hawkticehurst @misolori