Fixes#7929 and #12916
This PR adds [safe alignment
utilities](https://www.stefanjudis.com/today-i-learned/safe-unsafe-alignment-in-css-flexbox/)
to Tailwind 4. I opted to include them for every justify/align
content/items/self property, but only for the `end` and `center` values.
I know that it doesn't make sense for `start` (as the point of safe
alignment is to fall back to `start` when it overflows), but I'm not
sure about `space-between`, `space-around`, or other values. I certainly
never encountered a situation where I needed `safe` with those.
ebfde316e1