Don't create bare spacing utilities with invalid multiples

[philipp-spiess]

Closes #14960

When we moved to the --spacing multiples scale, we seemingly overlooked a bail that caused us to use non-numerical values as a spacing multiple. This caused the -translate-x-full and -translate-y-full utilities to treat full as a valid multiple in our spacing scale and created invalid CSS:

.-translate-x-full {
  --tw-translate-x: calc(var(--spacing) * -x-full);
  --tw-translate-y: calc(var(--spacing) * -x-full);
  translate: var(--tw-translate-x) var(--tw-translate-y);
}

Test plan

I reproduced the issue in our Vite playground and then created a failing test case. It requires a --spacing @theme variable to be defined so I've added this as a test case now in the unit tests. I also audited all places that are using calc() and wrapping some numbers. In doing so I found a few other broken cases:

• -translate-x-full
• -translate-y-full
• -space-x-full
• -space-y-full
• -inset-full

I validated that the fix indeed works and no longer creates broken CSS definitions for these cases: