Fix UMD globals

[mstade]

Description

These changes aim to fix an issue with exporting UMD modules that depend on other modules. The issue and fix is explained more in-depth in babel/babel#4766.

Because the babel PR has yet to be accepted or discussed, we've decided to fork the relevant plugin to enable a release separate from Babel. This is unfortunate, and whenever babel merges babel/babel#4766 or otherwise fix this issue, we should move back to that plugin.

Motivation and Context

Without this, UMD modules that have dependencies on other UMD modules will break.

How Was This Tested?

This change is both in babel and in ez-build. Tests were added to the babel PR, but remains to be added to this.

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My change follows the style of this project
• [ ] My change requires a change to the documentation
• [ ] I have updated the documentation accordingly
• [x] I have read the contribution guidelines
• [x] I have added tests to cover my changes
• [x] All new and existing tests passed

[codecov-io]

Current coverage is 87.68% (diff: 100%)

Merging #45 into master will decrease coverage by 0.26%

@@             master        #45   diff @@
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  Files             4         15    +11   
  Lines            83        268   +185   
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
+ Hits             73        235   +162   
- Misses           10         33    +23   
  Partials          0          0          

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