Move kernel baseline tests to front_end.

pkg/kernel/testcases/spec-mode/escape.baseline.txt

-library;
-import self as self;
-import "dart:core" as core;
-
-class A extends core::Object {
-  field dynamic field = null;
-  constructor •() → void
-    : super core::Object::•()
-    ;
-}
-class B extends core::Object {
-  field dynamic field = null;
-  constructor •() → void
-    : super core::Object::•()
-    ;
-}
-class C extends core::Object {
-  constructor •() → void
-    : super core::Object::•()
-    ;
-  operator ==(dynamic x) → dynamic
-    return false;
-}
-class X extends core::Object implements self::A, self::B {
-  field dynamic field = null;
-  constructor •() → void
-    : super core::Object::•()
-    ;
-}
-static method useAsA(self::A object) → void {
-  dynamic _ = object.field;
-}
-static method useAsB(self::B object) → void {
-  dynamic _ = object.field;
-  self::escape(object);
-}
-static method escape(dynamic x) → void {
-  x.==(null) ? x = "" : null;
-  x.==(null) ? x = 45 : null;
-  if(!(x is core::int) && !(x is core::String)) {
-    x.field = 45;
-  }
-}
-static method main() → dynamic {
-  dynamic object = new self::X::•();
-  self::useAsA(new self::A::•());
-  self::useAsA(object);
-  self::useAsB(new self::B::•());
-  self::useAsB(object);
-}