Changed "unload" to "beforeunload" in extjs to avoid deprecation warning in developer console

[andrewcbi]

Description (*)

Updated the unload calls to be beforeunload in extjs (removes deprecation warning in chrome console).

Manual testing scenarios (*)

1. Open console in chrome when in backend admin section.
2. Deprecated feature warning will be shown.
3. With this change the warning related to extjs no longer appears.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• Add yourself to contributors list

[fballiano]

tested and couldn't see any problem

[ADDISON74]

The description is not exactly suitable for the way of reproducing the error. Let's rephrase it.

If we access Backend > CMS then we edit any page, in the tab Issues it is displayed the following breaking change:

Deprecated feature used
Unload event listeners are deprecated and will be removed.
1 source
prototype.js:7020

Applying this PR the message is no longer displayed.

PS - In the future, when you create a new branch for a PR, please don't call it "main".