Fix missing variables for UMD and IIFE builds

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:
Resolves #3723

Description

There was a rendering issue that was not popping up in tests due to an interaction between different builds, which is fixed here.

[rollup-bot]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#gh-3723-missing-umd-variables

or load it into the REPL:
https://rollupjs.org/repl/?circleci=12562

[codecov]

Codecov Report

Merging #3724 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3724   +/-   ##
=======================================
  Coverage   96.97%   96.97%           
=======================================
  Files         184      184           
  Lines        6408     6409    +1     
  Branches     1855     1856    +1     
=======================================
+ Hits         6214     6215    +1     
  Misses        103      103           
  Partials       91       91           

Impacted Files	Coverage Δ
src/Chunk.ts	100.00% <100.00%> (ø)

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