Better concurrency handling for search JS script loading

[GuillaumeGomez]

As discussed in #118961.

Does it solve your issue @notriddle, or did I completely misunderstand?

r? @notriddle

[rustbot]

Some changes occurred in HTML/CSS/JS.

cc @GuillaumeGomez, @jsha

[notriddle]

That works, and I think you did understand the problem, but it seems even more complicated than what we're doing now. It still involves storing the searchIndex in a global variable, and it's still takes a slightly different code path depending on which order the files load in, so there's an opportunity for future changes to add a race condition.

The code in master, right now, works fine. This doesn't seem any more robust or otherwise better.

[GuillaumeGomez]

Agreed. I'll close this PR and still send a cleanup I discovered.

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

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---
info: ES-Check: there were no ES version matching errors!  🎉
+ eslint -c ../src/librustdoc/html/static/.eslintrc.js ../src/librustdoc/html/static/js/externs.js ../src/librustdoc/html/static/js/main.js ../src/librustdoc/html/static/js/scrape-examples.js ../src/librustdoc/html/static/js/search.js ../src/librustdoc/html/static/js/settings.js ../src/librustdoc/html/static/js/src-script.js ../src/librustdoc/html/static/js/storage.js

/checkout/src/librustdoc/html/static/js/main.js
  191:29  error  Strings must use doublequote  quotes
  191:38  error  Strings must use doublequote  quotes
/checkout/src/librustdoc/html/static/js/search.js
/checkout/src/librustdoc/html/static/js/search.js
  3357:5  error  'runSearchIfFullyLoaded' is not defined  no-undef

✖ 3 problems (3 errors, 0 warnings)
  2 errors and 0 warnings potentially fixable with the `--fix` option.
  local time: Fri Dec 15 15:47:21 UTC 2023
  network time: Fri, 15 Dec 2023 15:47:21 GMT
##[error]Process completed with exit code 1.
Post job cleanup.