[CSS] `touch-action:pinch-zoom` support

[chrisdavidmills]

Acceptance criteria

1. • The listed features are documented sufficiently on MDN
2. • BCD is updated
3. • Interactive example and data repos are updated if appropriate
4. • The content has been reviewed as needed

Features to document

1. touch-action:pinch-zoom support. Looks like this is documented fairly well, but the BCD is a bit complex and needs updating.

Related Gecko bugs

1. • Add support for touch-action:pinch-zoom

For folks helping with Firefox-related documentation features — make sure above AC have been done, but also:

• Set bugs to dev-doc-complete
• Add entry to Firefox release notes if feature is enabled in release
• Add entry to Firefox experimental features page if feature is not yet enabled in release

[chrisdavidmills]

Reviewed, looks great. Closing!