Perform type inference on explicitly typed fields.

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

 library test;
 import self as self;
 import "dart:core" as core;
 
 class A extends core::Object {
   constructor •() → void
     : super core::Object::•()
     ;
   operator ~() → core::int
     return 1;
   operator unary-() → core::double
     return 2.0;
 }
 static field self::A a = new self::A::•();
-static field core::int v_complement = self::a.~();
-static field core::double v_negate = self::a.unary-();
+static field core::int v_complement = self::a.{self::A::~}();
+static field core::double v_negate = self::a.{self::A::unary-}();
 static method main() → dynamic {
   self::a;
   self::v_complement;
   self::v_negate;
 }