External Libraries: Update Plupload from 2.1.9 to 2.3.6.

This change also updates the MoxieJS dependency from 1.3.5 to 1.5.7, converts Plupload to a dependency in NPM, and integrates all relevant parts into the build process.

For a full list of upstream changes, see https://github.com/moxiecode/plupload/compare/v2.1.9...v2.3.6.

Props desrosj, hareesh-pillai.
Fixes #48277.
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