feat: fall back to module resolution when relative imports fail

[kherock]

Resolves #187. These changes enable developers to import sass by the same resolution logic that webpack's sass-loader uses.

[codecov]

Codecov Report

Merging #198 (3efaa44) into main (11fcf2d) will decrease coverage by 0.08%.
The diff coverage is 95.45%.

@@            Coverage Diff             @@
##             main     #198      +/-   ##
==========================================
- Coverage   99.63%   99.54%   -0.09%     
==========================================
  Files          36       36              
  Lines        1083     1089       +6     
  Branches      318      319       +1     
==========================================
+ Hits         1079     1084       +5     
- Misses          4        5       +1     

Impacted Files	Coverage Δ
src/loaders/sass/importer.ts	96.42% <95.00%> (-3.58%)	⬇️
src/utils/url.ts	100.00% <100.00%> (ø)

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[kherock]

@Anidetrix (awesome to see that you're back!) I just rebased this and would appreciate getting it in an upcoming release. The implementation here should be fully backwards-compatible.

[leximarie]

@Anidetrix This would be very helpful to get in a release