Ensure that `PDFFindBar._adjustWidth` is called in all situations where the width of the findbar might have changed

After PR 8394, where the l10n service was converted to be asynchronous, we're no longer calling `_adjustWidth` after updating the `findMsg` label. Hence it's currently possible that the width of the findbar won't be correct. The solution is simple though, just call `_adjustWidth` after the `findMsg` label has been (asynchronously) updated.

Another existing issue, which was an oversight in PR 8132, is that `PDFFindBar.updateResultsCount` may be called directly from `PDFFindController`. In that case, we're not calling `_adjustWidth` at all, which means that the findbar may also not have the correct width.
The simple solution here is to always call `_adjustWidth` at the end of `updateResultsCount` (which is why we no longer need the `_adjustWidth` call at the end of `updateUIState`).

web/pdf_find_bar.js

@@ -140,10 +140,10 @@ class PDFFindBar {
     this.findField.setAttribute('data-status', status);
     Promise.resolve(findMsg).then((msg) => {
       this.findMsg.textContent = msg;
+      this._adjustWidth();
     });
 
     this.updateResultsCount(matchCount);
-    this._adjustWidth();
   }
 
   updateResultsCount(matchCount) {
@@ -160,6 +160,9 @@ class PDFFindBar {
       this.findResultsCount.textContent = matchCount.toLocaleString();
       this.findResultsCount.classList.remove('hidden');
     }
+    // Since `updateResultsCount` may be called from `PDFFindController`,
+    // ensure that the width of the findbar is always updated correctly.
+    this._adjustWidth();
   }
 
   open() {