If you correctly understood that the built-in functionality is close to what you are looking for: From the context menu of the file, select Compare With > Local History... I do not know the temporary function (this sounds good); here you get a list of versions and timestamps. These are discrete versions, therefore they are not "living" (both in each individual letter and in the change).
In Preferences > General > Editors > Text Editors > Quick Diff Enable quick diff, Show differences in overview ruler , live viewing is possible. Then the developer sees the changes as colored blocks in the overview bar on the left in the editor window. You can even set the link, either the last saved local version, or the basic version of SCM. The first display is reset when saved.
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