jsonschema: add more schema fields

Add additional fields to Schema which are mentioned in the spec but
do not affect validation.

Change-Id: I89488261a00c207d01cd7fc59d782f43692fe528
Reviewed-on: https://go-review.googlesource.com/c/tools/+/674976
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Jonathan Amsterdam <jba@google.com>

jsonschema/validate_test.go

@@ -42,14 +42,12 @@ func TestValidate(t *testing.T) {
 	for _, file := range files {
 		base := filepath.Base(file)
 		t.Run(base, func(t *testing.T) {
-			f, err := os.Open(file)
+			data, err := os.ReadFile(file)
 			if err != nil {
 				t.Fatal(err)
 			}
-			defer f.Close()
-			dec := json.NewDecoder(f)
 			var groups []testGroup
-			if err := dec.Decode(&groups); err != nil {
+			if err := json.Unmarshal(data, &groups); err != nil {
 				t.Fatal(err)
 			}
 			for _, g := range groups {