Fix performance regression when a file is imported by many importers

[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 #3640

Description

In Rollup 2.9.0, new properties importers and dynamicImporters were added to this.getModuleInfo. While the graph was built, these properties were extended ver often for some files (in the example in #3640, react and another file were imported both by more than 5000 files).
These properties were also sorted and the logic was built in a way so that the properties were sorted after any new importer was added. Now if you add 5000 properties to an array and sort the array after each added property, this does not scale well.

This PR fixes this regression by only sorting when the this.getModuleInfo is actually called.

[rollup-bot]

Thank you for your contribution! ❤️

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

npm install rollup/rollup#fix-load-performance-regression

or load it into the REPL:
https://rollupjs.org/repl/?circleci=11987

[codecov]

Codecov Report

Merging #3641 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3641   +/-   ##
=======================================
  Coverage   96.54%   96.54%           
=======================================
  Files         183      183           
  Lines        6244     6244           
  Branches     1830     1832    +2     
=======================================
  Hits         6028     6028           
  Misses        107      107           
  Partials      109      109           

Impacted Files	Coverage Δ
src/Graph.ts	100.00% <ø> (ø)
src/ModuleLoader.ts	100.00% <ø> (ø)
src/ast/nodes/MemberExpression.ts	98.30% <100.00%> (ø)
src/utils/escapeId.ts	100.00% <100.00%> (ø)

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