Add utils for page and component layout

[daviddossett]

Feature/component description

Investigate need for utils that aid extension authors when laying out pages and components.

The main value prop of providing these utils is to avoid authors hardcoding one-off values for common scenarios like form stack spacing, grid layouts, and more.

[christian-bromann]

Just started to use this toolkit to build a configuration view and was looking for some sort of form components similar to https://bendera.github.io/vscode-webview-elements/components/vscode-form-container/ that matches the VSCode styleguide.

[daviddossett]

Thanks @christian-bromann! Could you create an issue with the component request? Interested in learning more about what you're looking to do here 👍