Fix StackBlitz examples needing docs CSS

[julien-deramond]

Reference #36391

Originally I wanted to be able to load only _component-examples.scss and only when needed. The main issue is that it contains Sass variables defined in other Sass files; including files in the framework.

It will be less obvious for the users but the only other way I found so far is to load directly in the index.html our docs.css...

Any other ideas?

Fixed use cases

• All examples in Layout > Grid (none of them displayed correctly the colored rectangles)
• All examples in Layout > Columns (none of them displayed correctly the colored rectangles)
• Layout > Gutters > No gutters
• All examples in Layout > CSS Grid
• All examples in Content > Images
• All examples in Content > Figures
• Some examples in Forms > Form control that uses .bd-example in order to add margin tops between form controls.
• Components > Alerts > Icons
• Components > Breadcrum > Dividers
• All examples in Components > Card that hadn't centered text in images
• All examples in Components > Carousel that hadn't centered text in images
• Components > Popovers > Custom popovers
• Components > Tooltips > Custom tooltips
• All examples in Helpers > Ratio that display gray rectangles
• Most of the examples in Utilities > Borders
• All examples in Utilities > Flex
• Examples in Utilities > Position with black squares

[mdo]

Loading the docs makes sense to me since that's what we build and publish. Adding a separate stylesheet would be an extra HTTP request. Alternatively we can try to build everything for the snippets with local <style> tags, but that would be messy and repetitive.

Just gives extra motivation to reduce the docs/examples CSS as much as possible.