fix: make themeVariables typesafe

[ad1992]

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Resolves #

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 30 lines in your changes missing coverage. Please review.

Project coverage is 5.86%. Comparing base (b263164) to head (33eaeb2).
Report is 6 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #5631   +/-   ##
=======================================
  Coverage     5.86%   5.86%           
=======================================
  Files          274     273    -1     
  Lines        41086   41075   -11     
  Branches       488     512   +24     
=======================================
  Hits          2408    2408           
+ Misses       38678   38667   -11     

Flag	Coverage Δ
unit	5.86% <0.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
packages/mermaid/src/diagrams/xychart/xychartDb.ts	0.00% <0.00%> (ø)
packages/mermaid/src/diagrams/pie/pieRenderer.ts	0.00% <0.00%> (ø)
.../mermaid/src/diagrams/quadrant-chart/quadrantDb.ts	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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Build	Status	Details	Updated (UTC)
default (Inspect)	✅ No changes detected	-	Jul 9, 2024, 7:47 AM

[ad1992]

Just type changes so hopefully should be easy to merge, cc @sidharthv96

[ad1992]

EDIT: I am running into more TS errors so will push for the fixes soon