Use pretty-simple to format native output.

Previously we used our own homespun formatting.  But this
produces over-long lines that aren't ideal for diffs in tests.
Easier to use something off-the-shelf and standard.

Closes #7580.

Performance is slower by about a factor of 10, but this isn't
really a problem because native isn't suitable as a serialization
format. (For serialization you should use json, because the reader
is so much faster than native.)

1 files changed, 36 insertions, 2 deletions

diff --git a/test/command/5700.md b/test/command/5700.md
index 64f99c862..ca8ab19fd 100644
--- a/test/command/5700.md
+++ b/test/command/5700.md
@@ -1,6 +1,40 @@
 ```
 % pandoc -t native -s --metadata-file command/5700-metadata-file-1.yml --metadata-file command/5700-metadata-file-2.yml
 ^D
-Pandoc (Meta {unMeta = fromList [("desc",MetaInlines [Str "Both",Space,Str "of",Space,Str "these",Space,Str "files",Space,Str "should",Space,Str "be",Space,Str "loaded."]),("title",MetaInlines [Str "Multiple",Space,Str "metadata",Space,Str "files",Space,Str "test"])]})
-[]
+Pandoc
+  ( Meta
+    { unMeta = fromList
+      [
+        ( "desc"
+        , MetaInlines
+          [ Str "Both"
+          , Space
+          , Str "of"
+          , Space
+          , Str "these"
+          , Space
+          , Str "files"
+          , Space
+          , Str "should"
+          , Space
+          , Str "be"
+          , Space
+          , Str "loaded."
+          ]
+        )
+      ,
+        ( "title"
+        , MetaInlines
+          [ Str "Multiple"
+          , Space
+          , Str "metadata"
+          , Space
+          , Str "files"
+          , Space
+          , Str "test"
+          ]
+        )
+      ]
+    }
+  ) []
 ```