Additional customization for --text-* theme variables

[clearasvodka]

With ability to customize --text-* theme variables and provide line-height, letter-spacing, and font-weight values alongside with a font size, would be nice to add text-transform utility.

@theme {
  --text-subheader: 0.75rem;
  --text-subheader--line-height: 1rem;
  --text-subheader--letter-spacing: 0.25rem;
  --text-subheader--font-weight: 600;
  --text-subheader--text-transform: uppercase;
}

Will be very handy if you already heave typography styles in your Design System with uppercase style (happens quite often) and wanted to use it just by triggering your custom class.

For example,

<div class="text-subheader">
  This is subheader.
</div>

And have this as a result:

#### THIS IS SUBHEADER.