Add placeholder classes to remaing utils

Status: **Opened for Review**
Reviewers: @kpeatt @ry5n @avelinet @cole-sanderson @mlworks @nastiatikk 
JIRA: **CSOPS-954**

## Changes
- Add placeholder classes (i.e. `$u-width-1of3`) to all utilities
It's more of an internal placeholder to avoid writing out flex initial in each of the above classes. Not expected to be used on its own.

The fix itself is really invisible to the person using the utility so if they have to apply it themselves it's likely that they'd miss it or forget it. This ensures the fix is applied to all extensions of the above utilities.