Stacks with Gaps don't have gaps in all supported browsers (e.g. iOS 12)

Created by: coliff

The new Stacks helpers (https://getbootstrap.com/docs/5.1/helpers/stacks/) are neat, but they don't work in all Bootstrap-supported browsers due to using Flexbox Gap which doesn't have wide browser support. https://caniuse.com/flexbox-gap

The Gap Spacing Utilities (https://getbootstrap.com/docs/5.1/utilities/spacing/#gap) are fine in iOS 12.5.4 since they use Grid Gap which is better supported.

I wonder if there should be a compatibility warning added to the Stacks docs page.