test: fix && update flaky snapshots

[mattlewis92]

Notable changes:

• removed the webpack manifest from snapshots to remove noise
• wrapped the loader with a hack to force the resourcePath to be consistent across builds so the instrumented output is always the same

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@5a1c4e8). Click here to learn what that means. The diff coverage is n/a.

@@           Coverage Diff           @@
##             master    #66   +/-   ##
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  Coverage          ?   100%           
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  Files             ?      2           
  Lines             ?      6           
  Branches          ?      0           
=======================================
  Hits              ?      6           
  Misses            ?      0           
  Partials          ?      0

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[mattlewis92]

@michael-ciniawsky done!

[joshwiens]

Ship it @michael-ciniawsky