Implement type inference of getters/setters based on inheritance.

pkg/front_end/testcases/inference/infer_getter_from_later_inferred_getter.dart.strong.expect

+library test;
+import self as self;
+import "dart:core" as core;
+
+class A extends core::Object implements self::B {
+  constructor •() → void
+    : super core::Object::•()
+    ;
+  get x() → core::int
+    return self::f();
+}
+abstract class B extends core::Object implements self::C {
+  constructor •() → void
+    : super core::Object::•()
+    ;
+  abstract get x() → core::int;
+}
+abstract class C extends core::Object {
+  constructor •() → void
+    : super core::Object::•()
+    ;
+  abstract get x() → core::int;
+}
+static method f() → dynamic
+  return null;
+static method main() → dynamic {}