Remove OS-specific behaviour

[felixfbecker]

This removes the check for os.platform and replaces it with inspecting the incoming file path instead.

[codecov]

Codecov Report

Merging #290 into master will increase coverage by 0.19%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #290      +/-   ##
==========================================
+ Coverage   59.41%   59.61%   +0.19%     
==========================================
  Files          14       14              
  Lines        2134     2132       -2     
  Branches      349      349              
==========================================
+ Hits         1268     1271       +3     
+ Misses        713      710       -3     
+ Partials      153      151       -2

Impacted Files	Coverage Δ
src/typescript-service.ts	71.37% <ø> (ø)	⬆️
src/project-manager.ts	82.72% <100%> (+1.2%)	⬆️
src/memfs.ts	88.23% <0%> (+1.17%)	⬆️

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