Big number component needs a fix for bad suffix positioning

[matthillco]

While working on print styles for the gem components, I noticed that the screen styles for the big_number component would need to be updated to match the print styles I wanted to apply.

This is because the screen styles for the suffix are broken: they don't work correctly with different types of suffix, for example % or letters. Notice how the + symbol looks OK, but the % and M are too low:

However I didn't want to refactor the screen styles as part of the print work, as it was out of scope, so this issue is a place to record it.

In the print styles work, I used vertical-align: unset on .gem-c-big-number__suffix to fix the incorrect vertical centring of other characters, which you can see if you use dev tools to change the + in the Component Guide Preview Example to %, £, M etc.

That's not necessarily the right fix, but might be a starting point for work based on this issue.