This change adds a new dialog component to Ink. It uses the new(ish) `<dialog>` element, which comes with a bunch of advantages. It can be shown as either a modal or non-modal. The dialog has three areas that can be customized: the title, the body, and actions. Actions can be separated into primary (right-aligned) and secondary (left-aligned). Actions can be specified either as regular buttons (or other elements), or as a special `DialogAction`. The `DialogAction` exists to prevent boilerplate for common cases, and has two modes: close or callback. If an action uses a callback and said callback returns a promise, all of the dialog's actions will be disabled while that promise runs, and the action that triggered it will be shown as busy. Testing Done: - Used dialog in storybook. - Used this from some code in Review Board.