cmd/compile: factor out Pkg, Sym, and Type into package types

- created new package cmd/compile/internal/types
- moved Pkg, Sym, Type to new package
- to break cycles, for now we need the (ugly) types/utils.go
  file which contains a handful of functions that must be installed
  early by the gc frontend
- to break cycles, for now we need two functions to convert between
  *gc.Node and *types.Node (the latter is a dummy type)
- adjusted the gc's code to use the new package and the conversion
  functions as needed
- made several Pkg, Sym, and Type methods functions as needed
- renamed constructors typ, typPtr, typArray, etc. to types.New,
  types.NewPtr, types.NewArray, etc.

Passes toolstash-check -all.

Change-Id: I8adfa5e85c731645d0a7fd2030375ed6ebf54b72
Reviewed-on: https://go-review.googlesource.com/39855
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/reflect_test.go

@@ -5,6 +5,7 @@
 package gc
 
 import (
+	"cmd/compile/internal/types"
 	"reflect"
 	"sort"
 	"testing"
@@ -12,24 +13,24 @@ import (
 
 func TestSortingByMethodNameAndPackagePath(t *testing.T) {
 	data := []*Sig{
-		&Sig{name: "b", pkg: &Pkg{Path: "abc"}},
+		&Sig{name: "b", pkg: &types.Pkg{Path: "abc"}},
 		&Sig{name: "b", pkg: nil},
 		&Sig{name: "c", pkg: nil},
-		&Sig{name: "c", pkg: &Pkg{Path: "uvw"}},
+		&Sig{name: "c", pkg: &types.Pkg{Path: "uvw"}},
 		&Sig{name: "c", pkg: nil},
-		&Sig{name: "b", pkg: &Pkg{Path: "xyz"}},
-		&Sig{name: "a", pkg: &Pkg{Path: "abc"}},
+		&Sig{name: "b", pkg: &types.Pkg{Path: "xyz"}},
+		&Sig{name: "a", pkg: &types.Pkg{Path: "abc"}},
 		&Sig{name: "b", pkg: nil},
 	}
 	want := []*Sig{
-		&Sig{name: "a", pkg: &Pkg{Path: "abc"}},
+		&Sig{name: "a", pkg: &types.Pkg{Path: "abc"}},
 		&Sig{name: "b", pkg: nil},
 		&Sig{name: "b", pkg: nil},
-		&Sig{name: "b", pkg: &Pkg{Path: "abc"}},
-		&Sig{name: "b", pkg: &Pkg{Path: "xyz"}},
+		&Sig{name: "b", pkg: &types.Pkg{Path: "abc"}},
+		&Sig{name: "b", pkg: &types.Pkg{Path: "xyz"}},
 		&Sig{name: "c", pkg: nil},
 		&Sig{name: "c", pkg: nil},
-		&Sig{name: "c", pkg: &Pkg{Path: "uvw"}},
+		&Sig{name: "c", pkg: &types.Pkg{Path: "uvw"}},
 	}
 	if len(data) != len(want) {
 		t.Fatal("want and data must match")