Move `tooltip_on_truncate` component to `gitlab-ui`

The following discussion from gitlab-ce!26564 should be addressed:

• @pslaughter started a discussion: (+1 comment)

  This is great! Thanks for looking into this @sarahghp! After testing locally, I think this is a safe move to make (but I'd like one more 👍 just to be safe).

  Since the requirement for this component actually comes from Pajamas, I'd recommend taking this another step further and moving TooltipOnTruncate to gitlab-ui. WDYT?