Replace beforeDestroy lifecycle option with beforeUnmount

[rak-phillip]

Summary

This replaces any remaining beforeDestroy lifecycle options with beforeDestroy, as mentioned in the Vue 3 migration guide[^1]. This change should also properly clean up the metrics poller, resolving the attached issue.

Fixes #12292

Occurred changes and/or fixed issues

• Replace beforeDestroy lifecycle option with beforeUnmount

Technical notes summary

I searched for instances of destroyed in Dashboard, but did not find any. I'm not aware of any other lifecycle options that would need to update at this point.

Areas or cases that should be tested

A lot of these lifecycle hooks are used in mixins. There's a good example to test in the associated issue, but also consider testing

• Sortable Table
• Resource Fetch
• Browser Tab Visibility

Areas which could experience regressions

This should be fixing regressions in each of the affected areas, as beforeDestroy is no longer a valid hook.

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
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• The PR template has been filled out
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• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes