Fix: Properly decode <, >, and & in mindmap node labels

[BambioGaming]

📑 Summary

This pull request fixes a rendering bug in Mermaid mindmap diagrams where characters like <, >, and & were incorrectly displayed as <, >, and & inside SVG elements.

This issue occurred because .text() in D3/SVG escapes HTML entities even when the decoded content is passed in. This PR addresses it by decoding these entities right before rendering.

Resolves #6396

📏 Design Decisions

Modified decodeEntities() function in utils.ts to replace common HTML entities (<, >, &) with their correct characters.

Applied decodeEntities() immediately before inserting text content into <tspan> elements via .text() in the updateTextContentAndStyles() function of createText.ts.

This approach ensures that the final text rendered in the SVG node is accurate and unescaped while maintaining full safety.

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 9 lines in your changes missing coverage. Please review.

Project coverage is 3.86%. Comparing base (936d107) to head (7776ce1).

Files with missing lines	Patch %	Lines
packages/mermaid/src/utils.ts	0.00%	7 Missing ⚠️
packages/mermaid/src/rendering-util/createText.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #6406   +/-   ##
=======================================
  Coverage     3.86%   3.86%           
=======================================
  Files          412     411    -1     
  Lines        43189   43184    -5     
  Branches       664     664           
=======================================
  Hits          1670    1670           
+ Misses       41519   41514    -5     

Flag	Coverage Δ
unit	3.86% <0.00%> (+<0.01%)	⬆️

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

Files with missing lines	Coverage Δ
packages/mermaid/src/rendering-util/createText.ts	0.50% <0.00%> (ø)
packages/mermaid/src/utils.ts	17.89% <0.00%> (-0.20%)	⬇️

... and 1 file with indirect coverage changes

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Build	Status	Details	Updated (UTC)
default (Inspect)	⚠️ Changes detected (Review)	114 changed	Mar 25, 2025, 4:01 PM

[BambioGaming]

I’ve confirmed that decodeEntities() is only used in mindmap rendering logic. Other diagram types are unaffected. The Argos visual changes are expected and limited to corrected rendering in mindmap node labels.