cmd/api: include constant values

Update #5935

R=golang-dev, rsc, iant, dave
CC=golang-dev
https://golang.org/cl/13261050

src/cmd/api/goapi.go

@@ -690,16 +690,13 @@ func (w *Walker) emitObj(obj types.Object) {
 	switch obj := obj.(type) {
 	case *types.Const:
 		w.emitf("const %s %s", obj.Name(), w.typeString(obj.Type()))
-
+		w.emitf("const %s = %s", obj.Name(), obj.Val())
 	case *types.Var:
 		w.emitf("var %s %s", obj.Name(), w.typeString(obj.Type()))
-
 	case *types.TypeName:
 		w.emitType(obj)
-
 	case *types.Func:
 		w.emitFunc(obj)
-
 	default:
 		panic("unknown object: " + obj.String())
 	}

src/cmd/api/testdata/src/pkg/p1/golden.txt

+pkg p1, const A = 1
 pkg p1, const A ideal-int
+pkg p1, const A64 = 1
 pkg p1, const A64 int64
+pkg p1, const AIsLowerA = 11
 pkg p1, const AIsLowerA ideal-int
+pkg p1, const B0 = 2
 pkg p1, const B0 ideal-int
+pkg p1, const ConstChase2 = 11
 pkg p1, const ConstChase2 ideal-int
+pkg p1, const ConversionConst = 5
 pkg p1, const ConversionConst MyInt
+pkg p1, const FloatConst = 3/2
 pkg p1, const FloatConst ideal-float
+pkg p1, const StrConst = "foo"
 pkg p1, const StrConst ideal-string
 pkg p1, func Bar(int8, int16, int64)
 pkg p1, func Bar1(int8, int16, int64) uint64