feat: Extend ThemeBuilder with reference token processing

[jkuelz]

Issue #, if available:

Description of changes: This adds the official reference token API, which is part 1 of a series for theming improvements.
Next up:

• Css token value preservation
• Seed token API
• Color palette generation utilities

[ac9YAbqsd7e6]

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.43%. Comparing base (60f8181) to head (841035a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #126      +/-   ##
==========================================
+ Coverage   97.39%   97.43%   +0.04%     
==========================================
  Files          45       45              
  Lines        2150     2186      +36     
  Branches      409      402       -7     
==========================================
+ Hits         2094     2130      +36     
  Misses         56       56              

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[just-boris]

Approved with minor suggestions