[Meta] Fix intermittent issues in the integration tests

[timvandermeij]

Despite having fixed the most occurring intermittent failures in the integration tests (see the closed issues with the intermittent label) we unfortunately still have a few of them left that trigger from time to time. We should list and fix them. This issue is a meta issue for this effort.

The following intermittents have been found on the bots as of July 4th, 2024, which is after landing all previously identified improvements:

Name	OS	Logs	Fixed?
FreeText Editor Update a freetext and scroll must check that a freetext is still there after having updated it and scroll the doc (assertion failure)	Windows	http://54.193.163.58:8877/f1e92ac29cc3a65/output.txt	-
FreeText Editor Update a freetext and scroll must check that a freetext is still there after having updated it and scroll the doc (timeout)	Windows	http://54.193.163.58:8877/481c711563dfae6/output.txt	✅ #18418
Interaction in autoprint.pdf must check if printing is triggered when the document is open	Windows	http://54.193.163.58:8877/b48df120bbc7f5c/output.txt	✅ #18617
Interaction in bug1782564.pdf must check that charLimit is correctly set	Windows	http://54.193.163.58:8877/a58317de0521842/output.txt	✅ #18399
Highlight Editor Highlight and caret browsing must check that the caret can move a highlighted text (and others tracked in #18187 due to the additional context)	Windows	http://54.193.163.58:8877/60a667d8d66f476/output.txt	✅ #18574
Highlight Editor Highlight with the keyboard must check that some text has been highlighted	Linux	http://54.241.84.105:8877/8891dbe9fe88686/output.txt	-
FreeText Editor FreeText on several pages must check that first annotation is selected without errors	Windows	http://54.193.163.58:8877/2336ef073f32ba6/output.txt	-
Text layer Text selection using mouse when selecting over a link allows clicking the link after selecting	Windows	http://54.193.163.58:8877/08a1619a072581d/output.txt	✅ #18555
Stamp Editor New alt-text flow must check the new alt text flow (part 1)	Windows	http://54.193.163.58:8877/10dc1652d064ee2/output.txt	-
Stamp Editor New alt-text flow must check the new alt text flow (part 2)	Windows	http://54.193.163.58:8877/bdd22b640958b26/output.txt	-
Interaction in issue15092.pdf must check that a values is correctly updated on a field and its siblings	Linux / Windows	http://54.241.84.105:8877/2277869b1c75180/output.txt / http://54.193.163.58:8877/4ced5711a1d31ee/output.txt	✅ #18624

[timvandermeij]

Note to self, the following is useful for reproducing scripting-related intermittents locally:

diff --git a/web/pdf_scripting_manager.js b/web/pdf_scripting_manager.js
index 63d08c604..68d1b8a21 100644
--- a/web/pdf_scripting_manager.js
+++ b/web/pdf_scripting_manager.js
@@ -177,6 +177,7 @@ class PDFScriptingManager {
         return; // The document was closed while the properties resolved.
       }
 
+      await new Promise(r => setTimeout(r, 2000));
       await this.#scripting.createSandbox({
         objects,
         calculationOrder,

diff --git a/src/pdf.sandbox.external.js b/src/pdf.sandbox.external.js
index 365d94a60..af646c29f 100644
--- a/src/pdf.sandbox.external.js
+++ b/src/pdf.sandbox.external.js
@@ -67,7 +67,7 @@ export class SandboxSupportBase {
     }
     try {
       args = this.exportValueToSandbox(args);
-      this.commFun(name, args);
+      this.win.setTimeout(this.commFun.bind(this, name, args), 1000);
     } catch (e) {
       this.win.console.error(e);  

3. Run the tests in a random order.

[timvandermeij]

For the FreeText Editor Update a freetext and scroll must check that a freetext is still there after having updated it and scroll the doc failure we collected interesting findings in #18415. Note in particular #18415 (comment) and the failed run at http://54.193.163.58:8877/0507814a8df56c1/output.txt where the base64-encoded PNGs are correct. If we comment out https://github.com/mozilla/pdf.js/blob/master/test/integration/freetext_editor_spec.mjs#L3647 we can reproduce the empty PNG issue locally.