yaml: Support multi document decode

Related to #1087

TODO:
Support encode via option?

format/yaml/yaml.go

@@ -36,18 +36,32 @@ func init() {
 
 func decodeYAML(d *decode.D) any {
 	br := d.RawLen(d.Len())
-	var r any
+
+	var vs []any
 
 	yd := yaml.NewDecoder(bitio.NewIOReader(br))
-	if err := yd.Decode(&r); err != nil {
-		d.Fatalf("%s", err)
-	}
-	if err := yd.Decode(new(any)); !errors.Is(err, io.EOF) {
-		d.Fatalf("trialing data after top-level value")
+	for {
+		var v any
+		err := yd.Decode(&v)
+		if err != nil {
+			if len(vs) == 0 {
+				d.Fatalf("%s", err)
+			} else if errors.Is(err, io.EOF) {
+				break
+			} else {
+				d.Fatalf("trialing data after document")
+			}
+		}
+
+		vs = append(vs, v)
 	}
 
 	var s scalar.Any
-	s.Actual = gojqx.Normalize(r)
+	if len(vs) == 1 {
+		s.Actual = gojqx.Normalize(vs[0])
+	} else {
+		s.Actual = gojqx.Normalize(vs)
+	}
 
 	switch s.Actual.(type) {
 	case map[string]any,