BUG: Fix inference of node_modules for loader prefixes.

[ryan-roemer]

Part of #79

• BUG: A loader in the identifier field would incorrectly have all modules inferred "as a node_modules file", even if not. Implements a naive loader stripping heuristic to correctly assess if node_modules or real application source.
• Optimizes internal calls to _isNodeModules() from 2 to 1 for better performance.

[codecov[bot]]

Codecov Report

Merging #99 into master will increase coverage by 0.5%. The diff coverage is 95.65%.

@@            Coverage Diff            @@
##           master      #99     +/-   ##
=========================================
+ Coverage   90.43%   90.93%   +0.5%     
=========================================
  Files          14       12      -2     
  Lines         669      651     -18     
  Branches      107      106      -1     
=========================================
- Hits          605      592     -13     
+ Misses         38       33      -5     
  Partials       26       26

Impacted Files	Coverage Δ
src/lib/actions/base.ts	92.3% <95.65%> (+1.28%)	:arrow_up:
src/lib/util/files.ts	86.66% <0%> (-4.64%)	:arrow_down:
src/lib/util/strings.ts	100% <0%> (ø)	:arrow_up:
src/lib/index.ts
src/lib/interfaces/modules.ts
src/lib/actions.ts	100% <0%> (+33.33%)	:arrow_up:

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