Remove whitespace generation (#5833)

* Remove whitespace generation and rely on default printing

Changes to printing:
* Add newline after last empty SwitchCase
* Add newlines around block comments if they are non-flow comments or contain newlines

* Fix a few more fixtures

packages/babel-traverse/test/fixtures/comments/attachment/expected.js

@@ -2,19 +2,31 @@
 {
   hasPrev;
   /* top */
-  /* left */ /* right */
+
+  /* left */
+
+  /* right */
+
   /* bottom */
 }
 {
   /* top */
-  /* left */ /* right */
+
+  /* left */
+
+  /* right */
+
   /* bottom */
   hasNext;
 }
 {
   hasPrev;
   /* top */
-  /* left */ /* right */
+
+  /* left */
+
+  /* right */
+
   /* bottom */
   hasNext;
 }