Actually unparse field names

Instead of just wrapping in "".

interpreter.go

@@ -591,9 +591,7 @@ func (i *interpreter) manifestJSON(trace *TraceElement, v value, multiline bool,
 				buf.WriteString(prefix)
 				buf.WriteString(indent2)
 
-				buf.WriteString("\"")
-				buf.WriteString(fieldName)
-				buf.WriteString("\"")
+				buf.WriteString(unparseString(fieldName))
 				buf.WriteString(": ")
 
 				// TODO(sbarzowski) body.Loc()

testdata/escaped_fields.golden

@@ -0,0 +1,5 @@
+{
+   "\n\n": null,
+   "\"": null,
+   "'": null
+}

testdata/escaped_fields.input

@@ -0,0 +1,8 @@
+{
+  '"': null,
+  "'": null,
+  |||
+    
+    
+  |||: null,
+}