Mismatch between grid and flex for align-items

[kelunik]

Flex uses items-center [1] [2] while Grid uses align-items-center [3]. I think both should use align-items- as prefix, because just items- doesn't make it clear whether it's align-items or justify-items.

We stumbled upon this while using align-items-center and changing it to align-items-baseline, because align-items-baseline doesn't exist in the Grid version, just as items-baseline from Flex.

Additionally, the Grid version should probably use a variable map instead of hardcoding start, end, center, stretch like Flex does.

[tretapey]

Kind of breaking change if we change that.. let me think how can we avoid it to break sites using the lib

[kelunik]

@tretapey The grid can use the same variable and expose all variants while flex offers the old and new variant. The usage of the old variant is then documented as deprecated. There's no need to immediately remove the old variant.

[tretapey]

@kelunik would you propose with a PR?