spike(891): add createFontFacesForTheme

[LukeFinch]

closes #000

What

1. Background - why this is needed
2. What did you do
3. What does the reviewers should expect

I have done:

• Written unit tests against changes
• Written functional tests against the component and/or NewsKit site
• Updated relevant documentation

I have tested manually:

• The feature's functionality is working as expected on Chrome, Firefox, Safari and Edge
• The screen reader reads and flows through the elements as expected.
• There are no new errors in the browser console coming from this PR.
• When visual test is not added, it renders correctly on different browsers and mobile viewports (Safari, Firefox, small mobile viewport, tablet)
• The Playground feature is working as expected

Before:

After:

Who should review this PR:

How to test:

[mutebg]

Everything looks good, in an ideal world we can export this directly from the publisher and createFontFacesForTheme to be part of the newskit-theme/title so that we can add the necessary types.

like type

type FontPaths = {
  'Poppins': string,
  'DM Mono': string,
};

that way we can guarantee the people provide all fonts.