Treeshake prototype modifications in classes

[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 #3587

Description

This will apply similar logic to classes as to functions so that adding a property to the prototype of an unused class does not count as a side-effect.

[rollup-bot]

Thank you for your contribution! ❤️

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

npm install rollup/rollup#gh-3587-treeshake-class-prototype-modifications

or load it into the REPL:
https://rollupjs.org/repl/?circleci=11434

[codecov]

Codecov Report

Merging #3598 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3598   +/-   ##
=======================================
  Coverage   96.35%   96.35%           
=======================================
  Files         180      180           
  Lines        6145     6147    +2     
  Branches     1801     1805    +4     
=======================================
+ Hits         5921     5923    +2     
  Misses        111      111           
  Partials      113      113           

Impacted Files	Coverage Δ
src/ast/nodes/shared/ClassNode.ts	100.00% <100.00%> (ø)

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