docs: use doxygenindex directive for src

[ReenigneArcher]

Description

Replace #1919

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

Branch Updates

LizardByte requires that branches be up-to-date before merging. This means that after any PR is merged, this branch
must be updated before it can be merged. You must also
Allow edits from maintainers.

• I want maintainers to keep my branch updated

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 8.96%. Comparing base (acd9ae6) to head (97916b7).
Report is 145 commits behind head on master.

Additional details and impacted files

@@          Coverage Diff           @@
##           master   #2726   +/-   ##
======================================
  Coverage    8.96%   8.96%           
======================================
  Files          94      94           
  Lines       17392   17392           
  Branches     8270    8270           
======================================
  Hits         1560    1560           
- Misses      12967   12968    +1     
+ Partials     2865    2864    -1     

Flag	Coverage Δ
Linux	6.79% <ø> (ø)
Windows	4.16% <ø> (ø)
macOS-12	10.04% <ø> (ø)
macOS-13	9.95% <ø> (ø)
macOS-14	10.24% <ø> (ø)

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see 23 files with indirect coverage changes