jj: Update delta diff settings

Remove deprecated 'ui.diff.format' setting and replace with
'ui.diff-formatter'.

Use the time to also ONLY set up delta as the diff and show command
pager using scopes (since I was perusing the jj discussions anyway).

This has the advantage that normal jj paging is done with `-FRX` as far
as I understand -- which means after we close out of the pager the
content remains on screen (-X). This is not the case with delta. So now,
the contents of e.g. the last log command should always stay on screen.

vcs/jj/config/jj/config.toml

@@ -13,10 +13,14 @@ private-commits = "description(glob-i:'WIP:*') | description(glob-i:'PRIVATE:*')
 [ui]
 default-command = "log"
 diff-editor = ["nvim", "-c", "DiffEditor $left $right $output"]
-pager = "delta"
 
-[ui.diff]
-format = "git" # for the time being to use delta well
+# use delta as formatter but _only_ for diff and show
+# see: https://github.com/jj-vcs/jj/discussions/4690#discussioncomment-12388965
+[[--scope]]
+--when.commands = ["diff", "show"]
+[--scope.ui]
+pager = "delta"
+diff-formatter = ":git"
 
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