fix(codemode): live Map/Set forEach, generator prototypes, repeated function declarations, delete on non-references - #50450

 const m = new Map([[1, "a"], [2, "b"]])
 m.forEach((v, k) => { if (k === 1) { m.delete(2); m.set(3, "c") } log(k) })
-1 2                      // walked a snapshot
+1 3                      // live, as in JS: deleted entries skipped, added ones visited

 function* g() {}
-g() instanceof g         // TypeError: no 'prototype' object
+g() instanceof g         // true; each generator function has its own prototype

 function f() { return 1 }
 function f() { return 2 }
-                         // TypeError: Identifier 'f' has already been declared
+f()                      // 2; last declaration wins, and `var f` may share the name

 const fact = function inner(n) { return n <= 1 ? 1 : n * inner(n - 1) }
-fact(4)                  // ReferenceError: Unknown identifier 'inner'
+fact(4)                  // 24; a named function expression sees its own name, read-only

-delete 0                 // TypeError: Only data fields may be deleted
+delete 0                 // true; the operand is evaluated. `delete variable` still throws.