bug symfony#50213 [ErrorHandler] Prevent conflicts with WebProfilerBundle’s JavaScript (MatTheCat)

This PR was merged into the 5.4 branch.

Discussion
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[ErrorHandler] Prevent conflicts with WebProfilerBundle’s JavaScript

| Q             | A
| ------------- | ---
| Branch?       | 5.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | Fix symfony#50108
| License       | MIT
| Doc PR        | N/A

ErrorHandler’s `exception.js` and WebProfilerBundle’s `base_js.html.twig` both expose a global `Sfjs` variable, which create conflicts (see linked issue e.g.).

As the exception page
- does not make use of `Sfjs`
- is not extensible

I updated `exception.js` to not create any global scope variable. I also removed `DOMContentLoaded` listeners as the script is run inline at the end of the document.

This PR stems from symfony#48037.
Hiding whitespaces will produce a much more readable diff.

Commits
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e331b28 Do not expose `Sfjs` as it is unused and conflicts with WebProfilerBundle’s

Author: fabpot