Add safe alignment utilities

[benface]

Fixes #7929 and #12916

This PR adds safe alignment utilities 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.