deprecate do: meaning do (): + misc cleanup (#20927)

* test disable do: block lambda lifting

* fix last test [skip ci]

* deprecate `do:` meaning `do ():` + misc cleanup

closes https://github.com/nim-lang/RFCs/issues/486

* oops

* fix

* no idea what could be causing nimsuggest failure other than this

* ensure ci works

tests/closure/tclosure_issues.nim

@@ -71,12 +71,12 @@ block tissue7104:
   proc sp(cb: proc())=
       cb()
 
-  sp:
+  sp do ():
       var i = 0
       echo "ok ", i
-      sp():
+      sp do ():
           inc i
           echo "ok ", i
-          sp do:
+          sp do ():
               inc i
               echo "ok ", i