Add type inference for assignments to properties.

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

+library test;
+import self as self;
+import "dart:core" as core;
+
+class A extends core::Object {
+  constructor •() → void
+    : super core::Object::•()
+    ;
+}
+class B extends self::A {
+  constructor •() → void
+    : super self::A::•()
+    ;
+  operator +(self::C v) → self::A
+    return null;
+  operator -(core::int i) → self::B
+    return null;
+  operator *(self::B v) → self::B
+    return null;
+  operator &(self::A v) → self::C
+    return null;
+}
+class C extends self::B {
+  constructor •() → void
+    : super self::B::•()
+    ;
+}
+class Test extends core::Object {
+  field self::B member = null;
+  constructor •() → void
+    : super core::Object::•()
+    ;
+  static method test(self::Test t) → void {
+    let final dynamic #t1 = t in #t1.==(null) ? null : #t1.{self::Test::member} = self::f<self::B>();
+    let final dynamic #t2 = t in #t2.==(null) ? null : #t2.{self::Test::member}.{core::Object::==}(null) ? #t2.{self::Test::member} = self::f<self::B>() : null;
+    let final dynamic #t3 = t in #t3.==(null) ? null : #t3.{self::Test::member} = #t3.{self::Test::member}.{self::B::+}(self::f<dynamic>());
+    let final dynamic #t4 = t in #t4.==(null) ? null : #t4.{self::Test::member} = #t4.{self::Test::member}.{self::B::*}(self::f<dynamic>());
+    let final dynamic #t5 = t in #t5.==(null) ? null : #t5.{self::Test::member} = #t5.{self::Test::member}.{self::B::&}(self::f<dynamic>());
+    let final dynamic #t6 = t in #t6.==(null) ? null : #t6.{self::Test::member} = #t6.{self::Test::member}.{self::B::-}(1);
+    let final dynamic #t7 = t in #t7.==(null) ? null : #t7.{self::Test::member} = #t7.{self::Test::member}.{self::B::-}(1);
+    self::B v1 = let final dynamic #t8 = t in #t8.==(null) ? null : #t8.{self::Test::member} = self::f<self::B>();
+    self::B v2 = let final dynamic #t9 = t in #t9.==(null) ? null : let final dynamic #t10 = #t9.{self::Test::member} in #t10.{core::Object::==}(null) ? #t9.{self::Test::member} = self::f<self::B>() : #t10;
+    self::A v3 = let final dynamic #t11 = t in #t11.==(null) ? null : #t11.{self::Test::member} = #t11.{self::Test::member}.{self::B::+}(self::f<dynamic>());
+    self::B v4 = let final dynamic #t12 = t in #t12.==(null) ? null : #t12.{self::Test::member} = #t12.{self::Test::member}.{self::B::*}(self::f<dynamic>());
+    self::C v5 = let final dynamic #t13 = t in #t13.==(null) ? null : #t13.{self::Test::member} = #t13.{self::Test::member}.{self::B::&}(self::f<dynamic>());
+    self::B v6 = let final dynamic #t14 = t in #t14.==(null) ? null : #t14.{self::Test::member} = #t14.{self::Test::member}.{self::B::-}(1);
+    self::B v7 = let final dynamic #t15 = t in #t15.==(null) ? null : let final dynamic #t16 = #t15.{self::Test::member} in let final dynamic #t17 = #t15.{self::Test::member} = #t16.{self::B::-}(1) in #t16;
+  }
+}
+static method f<T extends core::Object>() → self::f::T
+  return null;
+static method main() → dynamic {}