Do not count accessing members of an external namespace as side-effects.

[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:
#3999

Description

This solves a regression introduced in #3999 where accessing properties of external namespaces was considered side-effectful, preventing tree-shaking.

[rollup-bot]

Thank you for your contribution! ❤️

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

npm install rollup/rollup#no-namespace-access-side-effect

or load it into the REPL:
https://rollupjs.org/repl/?circleci=14576

[codecov]

Codecov Report

Merging #4001 (e06d6ff) into master (9c19865) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4001   +/-   ##
=======================================
  Coverage   97.24%   97.24%           
=======================================
  Files         191      191           
  Lines        6741     6742    +1     
  Branches     1967     1968    +1     
=======================================
+ Hits         6555     6556    +1     
  Misses         99       99           
  Partials       87       87           

Impacted Files	Coverage Δ
src/ast/variables/ExternalVariable.ts	100.00% <100.00%> (ø)

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[stefcameron]

@lukastaegert Thank you for this fix, it solved my issue!