chore(contented-pipeline): un-complicate getSanitizedPath parsing

[fuxingloh]

What this PR does / why we need it:

As per title.

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[codecov]

Codecov Report

Merging #635 (d14f1af) into main (0551e1b) will increase coverage by 6.42%.
Report is 75 commits behind head on main.
The diff coverage is 95.56%.

@@            Coverage Diff             @@
##             main     #635      +/-   ##
==========================================
+ Coverage   85.00%   91.42%   +6.42%     
==========================================
  Files          10       13       +3     
  Lines         420      548     +128     
  Branches       73      101      +28     
==========================================
+ Hits          357      501     +144     
+ Misses         63       47      -16     

Files	Coverage Δ
...ented-pipeline-jest-md/src/JestMarkdownPipeline.ts	100.00% <100.00%> (ø)
...ages/contented-pipeline-md/src/MarkdownPipeline.ts	86.84% <100.00%> (+1.54%)	⬆️
...contented-pipeline-md/src/plugins/RehypeHeading.ts	93.54% <ø> (+6.45%)	⬆️
...contented-pipeline-md/src/plugins/RehypeMermaid.ts	93.75% <ø> (+50.00%)	⬆️
...ntented-pipeline-md/src/plugins/RemarkCodeblock.ts	100.00% <100.00%> (ø)
...d-pipeline-md/src/plugins/RemarkDirectiveRehype.ts	100.00% <100.00%> (ø)
...es/contented-pipeline-md/src/plugins/RemarkLink.ts	100.00% <100.00%> (+28.57%)	⬆️
...ages/contented-processor/src/ContentedProcessor.ts	88.46% <100.00%> (+2.04%)	⬆️
...ages/contented-pipeline-md/src/UnifiedProcessor.ts	92.59% <96.15%> (+5.09%)	⬆️
...s/contented-pipeline-md/src/plugins/RehypeShiki.ts	96.77% <96.77%> (ø)
... and 2 more