Bug: `_rev` field overridden when `rev` field is present

[feliixx]

Hi, thanks for maintaining this great project ! While trying to update an old document with Fauxton recently I noticed a weird behavior:

Expected Behavior

• the _rev attribute should left untouched when viewing a doc even if the doc contains a rev field
• the rev field stays visible on the document if it is present (similar issue as https://github.com/apache/couchdb-fauxton/issues/1427 ?)

Current Behavior

• The _rev attribute is overwritten by the content of the rev field
• the rev field does not appear in the document

Steps to Reproduce (for bugs)

1. Create an empty document, and save it. _rev becomes 1-xxx
2. Open the doc in Fauxton, and update the document to add the field "rev": "1-xxx"
3. Save the doc, and open it again in the UI

=> the UI shows the document with the wrong _rev: {"_rev": "1-xxx"} instead of {"_rev": "2-xxx", "rev": "1-xxx"}

Context

• noticed while trying to update a document with Fauxton. The update kept failing with document update conflict (which is logical as the _rev was wrongly overwritten)

Your Environment

• Version used: CouchDB 3.3.3
• Browser Name and version: Chromium 124
• Operating System and version (desktop or mobile): Fedora 39 on desktop / server is running Rockylinux 9