feat: Allow expressions to be terminated/sequenced by ;

Note that ultimately a terminated sequence may have
   a slightly different semantics (applying streams
   to `_|_`, most likely) but for now they don't.

editor/Syntax.esv

@@ -20,6 +20,7 @@ menus
     
     action: "Format"          = editor-format (source)
     action: "Show parsed AST" = debug-show-aterm (source)
+    action: "Desugar AST"     = debug-desugar-fostr (source)
 
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