Include --default-transition-* variables in transition-* utility output

[adamwathan]

Fixes #14479.

Back in March we made a change to the transition-* utilities that inlined the values of the --default-transition-* variables to fix a bug where things would break if those variables didn't exist in your CSS. At the time though we weren't outputting CSS variables as part of the values of any utilities, for example bg-red-500 didn't actually reference the --color-red-500 variable.

We later changed that but missed this situation, so these variables were still inlined even though nothing else was.

This PR fixes that and makes things more consistent, so these variables will be used as expected unless using the @theme inline option, like with everything else.