Extend FlexBox/Grid rules

Is your feature request related to a problem? Please describe. I created a PR (#1157) for adding gap to the Grid package. However, I'm also seeing other attributes that I would use that can be added in the same PR.

Describe the solution you'd like Add attributes such as (object names)alignItems, alignContent, justifyItems, justifyContent, placeItems, placeContent, placeSelfto Grid.

I recognize that some of these overlap with the Flexbox API and work just fine without duplicating in Grid as well.

So, for brevity and avoiding duplication, placeItems,placeContent, and placeSelf would extend Flexbox Mozilla abstracts these rules as CSS Box Alignment module and apply to both Flexbox and Grid; applying a similar abstraction would be breaking and just adding the previously mentioned to Flexbox is satisfactory from my perspective.

I would amend and rename PR (#1157) or create a new if preferred.