Add ability to change type tokens in theme switcher

[joshblack]

In v10.7.0, we shipped support for type tokens in our themes. However, our theme panel in storybook only supports swapping out the color theme. In order to allow design to review how a component changes with respect to type changes, we will need to provide a way for designers to change the type for a given component story. This change could mean:

• Switching between productive and expressive themes
• Bumping the base font-size

[joshblack]

cc @laurenmrice do you have any preferences for the best way to expose this to help with reviewing that a component changes appropriately when type size changes?

[joshblack]

Working session notes

• The following type tokens:
  • caption01
  • label01
  • helperText01
  • bodyShort01
  • bodyLong01
  • bodyShort02
  • bodyLong02
  • code01
  • code02
  • heading01
  • productiveHeading01
  • heading02
  • productiveHeading02
• Values should be a dropdown with the following items:
  • 12/16
  • 14/20
  • 14/18
  • 14/20
  • 16/24
  • 16/22
  • 20/26
  • 28/36