fix: include user-defined tokens as app token source

[xitij2000]

Description

Currently, app tokens are limited by the tokens defined in the Paragon core and light themes, if a new token is defined by a custom theme, app tokens can't reference it.

This change includes the user-defined tokens as sources so custom themes with app tokens can use values from there.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.40%. Comparing base (9340b9c) to head (5a631c7).
⚠️ Report is 2 commits behind head on release-23.x.

Additional details and impacted files

@@              Coverage Diff              @@
##           release-23.x    #4303   +/-   ##
=============================================
  Coverage         94.40%   94.40%           
=============================================
  Files               242      242           
  Lines              4309     4309           
  Branches            981      981           
=============================================
  Hits               4068     4068           
  Misses              237      237           
  Partials              4        4           

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