Support browser-level lazy-loading for images

## Feature request
Support lazy-loading images
Reference: https://web.dev/browser-level-image-lazy-loading/

#### What problem does this feature solve?

For pages with many images, instead of loading all the images, using lazy-loading will allow the browser fetch images on demand.

#### What does the proposed API look like?
I think we can expose an lazy loading option, or enable it by default.

#### How should this be implemented in your opinion?
Add `loading=lazy` to `img` tags.

#### Are you willing to work on this yourself?
Not sure where to change.