fix(infrastructure): add the es5 @material/package/dist/mdc.package to externals

[moog16]

When we converted all our @ material package imports to point to the es5 files instead of the es6, this changed the filepaths. We also need to update the webpack external filepaths so it is not included in bundled javascript file.

[codecov-io]

Codecov Report

Merging #223 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #223   +/-   ##
======================================
  Coverage    98.8%   98.8%           
======================================
  Files          21      21           
  Lines         834     834           
  Branches       78      78           
======================================
  Hits          824     824           
  Misses         10      10

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