Change the Dict.prototype.getKeys method to return an iterator

This method is usually used with loops, and it should be a tiny bit more efficient to use an iterator directly rather than first iterating through ` Map`-keys to create a temporary `Array` that we finally iterate through at the call-site.

Note that the `getKeys` method is old code, and originally the `Dict` class stored its data in a regular `Object`, hence why the old code was written that way.

Author: Snuffleupagus

src/core/annotation.js

@@ -3398,7 +3398,7 @@ class ButtonWidgetAnnotation extends WidgetAnnotation {
         ? this.data.fieldValue
         : "Yes";
 
-    const exportValues = this._decodeFormValue(normalAppearance.getKeys());
+    const exportValues = this._decodeFormValue([...normalAppearance.getKeys()]);
     if (exportValues.length === 0) {
       exportValues.push("Off", yes);
     } else if (exportValues.length === 1) {

src/core/primitives.js

@@ -180,7 +180,7 @@ class Dict {
   }
 
   getKeys() {
-    return [...this._map.keys()];
+    return this._map.keys();
   }
 
   // No dereferencing.

test/unit/primitives_spec.js

@@ -276,7 +276,7 @@ describe("primitives", function () {
 
     it("should get all key names", function () {
       const expectedKeys = ["FontFile", "FontFile2", "FontFile3"];
-      const keys = dictWithManyKeys.getKeys();
+      const keys = [...dictWithManyKeys.getKeys()];
 
       expect(keys.sort()).toEqual(expectedKeys);
     });
@@ -337,7 +337,7 @@ describe("primitives", function () {
         xref: null,
         dictArray: [dictWithManyKeys, dictWithSizeKey, fontFileDict],
       });
-      const mergedKeys = mergedDict.getKeys();
+      const mergedKeys = [...mergedDict.getKeys()];
 
       expect(mergedKeys.sort()).toEqual(expectedKeys);
       expect(mergedDict.get("FontFile")).toEqual(testFontFile);
@@ -374,8 +374,8 @@ describe("primitives", function () {
       expect(mergedFontDict instanceof Dict).toEqual(true);
       expect(mergedSubFontDict instanceof Dict).toEqual(true);
 
-      const mergedFontDictKeys = mergedFontDict.getKeys();
-      const mergedSubFontDictKeys = mergedSubFontDict.getKeys();
+      const mergedFontDictKeys = [...mergedFontDict.getKeys()];
+      const mergedSubFontDictKeys = [...mergedSubFontDict.getKeys()];
 
       expect(mergedFontDictKeys).toEqual(["F1"]);
       expect(mergedSubFontDictKeys).toEqual(["F1", "F2", "F3"]);