fix: Warn on external navigation during editing

[ekcom]

What type of PR is this?

(REQUIRED)

• bug

What this PR does / why we need it:

• Provide a last-second warning when navigating
• Covers navigation which the current navigation on unsaved changes alert
  does not handle (before this, only internal redirection gave the alert)

Which issue(s) this PR fixes:

Fixes #2912

[ekcom]

Note: this currently will display the warning message (e.g., "Reload site? Changes you made may not be saved.") on the edit page even if no changes were made.

I am not sure how to efficiently detect any changes. Can't check JSON.stringify(props.recipe) === JSON.stringify(originalRecipe.value) during the beforeunload event, so would probably need an event listener for any changes in the form. This may not be worth the performance cost.

This feature still works and is ready.

[boc-the-git]

LGTM. Tested it a bit and does what it says on the tin. Nice work!

I do agree with what you've suggested, that there's some inconsistency with some of the other internal navigation/warnings (e.g. refreshing the page (new warning) is different to navigating to the timeline (old warning)), but importantly this does work and will stop people losing data.

Further enhancements are absolutely welcome! :)