XFA - Implement aspect property on image element

- it aims to fix issue #13634;
  - move some img-related functions in test/drivers.js in order to have images in xfa reftests.

src/core/xfa/template.js

@@ -2829,11 +2829,38 @@ class Image extends StringObject {
     if (this.transferEncoding === "base64") {
       const buffer = stringToBytes(atob(this[$content]));
       const blob = new Blob([buffer], { type: this.contentType });
+      let style;
+      switch (this.aspect) {
+        case "fit":
+        case "actual":
+          // TODO: check what to do with actual.
+          // Normally we should return {auto, auto} for it but
+          // it implies some wrong rendering (see xfa_bug1716816.pdf).
+          break;
+        case "height":
+          style = {
+            width: "auto",
+            height: "100%",
+          };
+          break;
+        case "none":
+          style = {
+            width: "100%",
+            height: "100%",
+          };
+          break;
+        case "width":
+          style = {
+            width: "100%",
+            height: "auto",
+          };
+          break;
+      }
       return HTMLResult.success({
         name: "img",
         attributes: {
           class: ["xfaImage"],
-          style: {},
+          style,
           src: URL.createObjectURL(blob),
         },
       });