implement map/lazyMap for list-encoding test for rechecking-based capture checker

[olhotak]

Note that uncommenting line 75 still fails pickling tests. The pickling error is a change in the position of term in a @Retains clause in an inferred type. The diff is:

--- before-pickling.txt	2021-09-30 10:28:28.654187136 +0200
+++ after-pickling.txt	2021-09-30 10:28:28.662186774 +0200
@@ -8924,9 +8924,9 @@
               ((v: 
                 (Unit => scala.Int) @retains(
                   <
-                    <[<f:scala.Int => scala.Int>@tests/run/list-encoding.scala<1200..1201> : scala.Any]:Seq[scala.Any]>@
-                      tests/run/list-encoding.scala<1200..1201>
-                  *:scala.Any*>@tests/run/list-encoding.scala<1200..1201>
+                    <[<f:scala.Int => scala.Int>@tests/run/list-encoding.scala<1201..1201> : scala.Any]:Seq[scala.Any]>@
+                      tests/run/list-encoding.scala<1201..1201>
+                  *:scala.Any*>@tests/run/list-encoding.scala<1201..1201>
                 )
               ) => 
                 ((s: C) => C) @retains(

The position changes from 1200..1201 to 1201..1201. This is inside the type inferred for val lazylist56 = ....