[Feature] Update style-dictionary config to generate themes

Description of Change

Updates style-dictionary build config to generate themes and cleans up exports. See `dist/\ folder in npm code tab to view output:

Generates themes.js file which exports a themes object that contains both dark and light themes
- These themes are filtered to have all of the primitive and "mode-less" semantic tokens and the addition of any tokens with either the OnLight or OnDark mode suffixes
- The OnLight/OnDark suffixes have been removed in the token names of each of the themes so that in the app, components can reference the token without the suffix, removing the need for if (isDarkMode) conditionals (i.e. Referencing theme.vadsColorFeedbackSurfaceInfo instead of Colors.vadsColorFeedbackSurfaceInfoOnLight. This will be made clearer in the follow-up PR (#361)
Moved Colors var from index.js into its own file colors.js
Updated index.js to import/export both Colors and themes
Refactor typing generations:
- New types/ folder contains colors.d.ts and theme.d.ts
- All types are imported/exported in index.d.ts
Add Prettier formatting that runs post build to clean up file formatting

Code reviewer validation:

General
- [x] PR is linked to ticket(s)
- [x] PR has changelog label applied if it's to be included in the changelog
- [x] Acceptance criteria:
  - All satisfied or
  - Documented reason for not being performed or
  - Split to separate ticket and ticket is linked by relevant AC(s)
- [x] Above PR sections adequately filled out
- [x] If any breaking changes, in accordance with the pre-1.0.0 versioning guidelines: a CU ticket has been created for the VA Mobile App detailing necessary adjustments with the package version that will be published by this ticket
Code
- [x] Tests are included if appropriate (or split to separate ticket)
- [x] New functions have proper TSDoc annotations

If changes warrant a new version per the versioning guidelines and the PR is approved and ready to merge: