redirect to referral URL on element save again + adjustment

[i-just]

Description

v5.9.0 initially shipped with #16140

We then chose to revert that change (via 0fd95b2) because it was causing some issues (#18404 and some additional ones we spotted in Commerce).

This PR restores the redirect mechanism from Brian’s original PR, with a tweak that ensures we only compare the referrer and request URIs (ignoring the query string, etc.).

I tested this against #18473, the scenario from #18404 and against the issue we noticed in Commerce.

Example of an issue we spotted in Commerce:

• create a product & fully save
• edit the product; create a draft (not a provisional one)
• switch back to the canonical & press “Save” (not the shortcut to save and continue)
• you land back on the draft edit page instead of on the products index page

Related issues

#18473