typeof(voidStmt) now works (#17807)

* `typeof(voidStmt)` now works
* remove typeOrVoid
* add condsyms, and reference cligen https://github.com/c-blake/cligen/pull/193
* fixup
* changelog [skip ci]
* fixup

tests/typerel/tvoid.nim

@@ -35,3 +35,64 @@ ReturnT[void]()
 echo ReturnT[string]("abc")
 nothing()
 
+block: # typeof(stmt)
+  proc fn1(): auto =
+    discard
+  proc fn2(): auto =
+    1
+  doAssert type(fn1()) is void
+  doAssert typeof(fn1()) is void
+  doAssert typeof(fn1()) isnot int
+
+  doAssert type(fn2()) isnot void
+  doAssert typeof(fn2()) isnot void
+  when typeof(fn1()) is void: discard
+  else: doAssert false
+
+  doAssert typeof(1+1) is int
+  doAssert typeof((discard)) is void
+
+  type A1 = typeof(fn1())
+  doAssert A1 is void
+  type A2 = type(fn1())
+  doAssert A2 is void
+  doAssert A2 is A1
+
+  when false:
+    # xxx: MCS/UFCS doesn't work here: Error: expression 'fn1()' has no type (or is ambiguous)
+    type A3 = fn1().type
+  proc bar[T](a: T): string = $T
+  doAssert bar(1) == "int"
+  doAssert bar(fn1()) == "void"
+
+  proc bar2[T](a: T): bool = T is void
+  doAssert not bar2(1)
+  doAssert bar2(fn1())
+
+  block:
+    proc bar3[T](a: T): T = a
+    let a1 = bar3(1)
+    doAssert compiles(block:
+      let a1 = bar3(fn2()))
+    doAssert not compiles(block:
+      let a2 = bar3(fn1()))
+    doAssert compiles(block: bar3(fn1()))
+    doAssert compiles(bar3(fn1()))
+    doAssert typeof(bar3(fn1())) is void
+    doAssert not compiles(sizeof(bar3(fn1())))
+
+  block:
+    var a = 1
+    doAssert typeof((a = 2)) is void
+    doAssert typeof((a = 2; a = 3)) is void
+    doAssert typeof(block:
+      a = 2; a = 3) is void
+
+  block:
+    var a = 1
+    template bad1 = echo (a; a = 2)
+    doAssert not compiles(bad1())
+
+  block:
+    template bad2 = echo (nonexistant; discard)
+    doAssert not compiles(bad2())