Allow floating label to take full width when floating (scaled down)

[terencehonles]

This change allows the floating label to expand its width as it's scaled down because the width: 100% as defined in https://github.com/twbs/bootstrap/pull/36327 will no longer be correct.

I'm not sure about the process for adding new variables and if this is acceptable. I also realize that / outside of calc(...) is deprecated but I don't see any uses of @use 'sass:math' in the codebase and calc(...) was complaining it was not allowed when running npm run test and I was not sure if I should modify an allowlist or what would be preferred here.