Add a getRawValues method, to Dict instances, to provide an easier way of getting all *raw* values

When the old `Dict.getAll()` method was removed, it was replaced with a `Dict.getKeys()` call and `Dict.get(...)` calls (in a loop).
While this pattern obviously makes a lot of sense in many cases, there's some instances where we actually want the *raw* `Dict` values (i.e. `Ref`s where applicable). In those cases, `Dict.getRaw(...)` calls are instead used within the loop. However, by introducing a new `Dict.getRawValues()` method we can reduce the number of (strictly unnecessary) function calls by simply getting the *raw* `Dict` values directly.

src/core/primitives.js

@@ -144,6 +144,11 @@ var Dict = (function DictClosure() {
       return Object.keys(this._map);
     },
 
+    // no dereferencing
+    getRawValues: function Dict_getRawValues() {
+      return Object.values(this._map);
+    },
+
     set: function Dict_set(key, value) {
       if (
         (typeof PDFJSDev === "undefined" ||