[api-minor] Replace the PromiseCapability with Promise.withResolvers()

This replaces our custom `PromiseCapability`-class with the new native `Promise.withResolvers()` functionality, which does *almost* the same thing[1]; please see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/withResolvers

The only difference is that `PromiseCapability` also had a `settled`-getter, which was however not widely used and the call-sites can either be removed or re-factored to avoid it. In particular:
 - In `src/display/api.js` we can tweak the `PDFObjects`-class to use a "special" initial data-value and just compare against that, in order to replace the `settled`-state.
 - In `web/app.js` we change the only case to manually track the `settled`-state, which should hopefully be OK given how this is being used.
 - In `web/pdf_outline_viewer.js` we can remove the `settled`-checks, since the code should work just fine without it. The only thing that could potentially happen is that we try to `resolve` a Promise multiple times, which is however *not* a problem since the value of a Promise cannot be changed once fulfilled or rejected.
 - In `web/pdf_viewer.js` we can remove the `settled`-checks, since the code should work fine without them:
     - For the `_onePageRenderedCapability` case the `settled`-check is used in a `EventBus`-listener which is *removed* on its first (valid) invocation.
     - For the `_pagesCapability` case the `settled`-check is used in a print-related helper that works just fine with "only" the other checks.
 - In `test/unit/api_spec.js` we can change the few relevant cases to manually track the `settled`-state, since this is both simple and *test-only* code.

---
[1] In browsers/environments that lack native support, note [the compatibility data](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/withResolvers#browser_compatibility), it'll be polyfilled via the `core-js` library (but only in `legacy` builds).

web/password_prompt.js

@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 
-import { PasswordResponses, PromiseCapability } from "pdfjs-lib";
+import { PasswordResponses } from "pdfjs-lib";
 
 /**
  * @typedef {Object} PasswordPromptOptions
@@ -64,10 +64,8 @@ class PasswordPrompt {
   }
 
   async open() {
-    if (this.#activeCapability) {
-      await this.#activeCapability.promise;
-    }
-    this.#activeCapability = new PromiseCapability();
+    await this.#activeCapability?.promise;
+    this.#activeCapability = Promise.withResolvers();
 
     try {
       await this.overlayManager.open(this.dialog);