feat(highlights): new Dimmed hl group for de-emphasized text #39505

Problem:
Many color schemes assume the Comment hl group is dim text and use it
for secondary text, decorations, or parts of UI. This is true for many
color schemes but not all.

Solution:
Introducing a new highlight group with a more specific meaning, similar
to Underlined or Ignore.

The new group links to Comment by default so the behavior is unchanged
for color schemes that don't define it.

runtime/lua/vim/_inspector.lua

@@ -186,7 +186,7 @@ function vim.show_pos(buf, row, col, filter)
       append('   ')
     end
     if comment then
-      append(comment, 'Comment')
+      append(comment, 'Dimmed')
     end
     nl()
   end
@@ -244,7 +244,7 @@ function vim.show_pos(buf, row, col, filter)
         item(extmark.opts, extmark.ns)
       else
         append('  - ')
-        append(extmark.ns, 'Comment')
+        append(extmark.ns, 'Dimmed')
         nl()
       end
     end