Replace a bunch of Array.prototype.forEach() cases with for...of loops instead

Using `for...of` is a modern and generally much nicer pattern, since it gets rid of unnecessary callback-functions. (In a couple of spots, a "regular" `for` loop had to be used.)

src/display/font_loader.js

@@ -61,9 +61,9 @@ class BaseFontLoader {
   }
 
   clear() {
-    this.nativeFontFaces.forEach(nativeFontFace => {
+    for (const nativeFontFace of this.nativeFontFaces) {
       this._document.fonts.delete(nativeFontFace);
-    });
+    }
     this.nativeFontFaces.length = 0;
 
     if (this.styleElement) {