Re-enable mention intermittent failed cases

[aagash-ni]

Pull Request

🤨 Rationale

Issue: #2219

We are re-enabling tests that were previously disabled due to intermittent failures and disabling only in the Firefox environment, as the issue occurred only once during four days of testing. Additionally, there were other cases that are validating the same mention workflow, which has been successfully running in Firefox.

After conducting tests in a loop environment on GitHub agents, the tests did not fail with the same error.

Please refer to the bug discussion for all the pipeline checks: Bug 2787273 - Intermittent failures in the Rich Text Editor for Mention support.

Following this, we will monitor for any related failures and have created a TD to track the skipped Firefox browser tests.

👩‍💻 Implementation

Re-enabled the disabled test case.

Update:

1. For test should show mention popup for multiple mention configuration elements:
   1. Instead of committing the @ mention node, remove the @ and add ! to verify other mention type list options and popup visibility.
   2. The test can now verify the list options for multiple mentions by opening the popup.
2. For test Serialize rich text editor content to its respective markdown Mention node:
   1. Update the clickMentionListboxOption to focus on the editor before committing the mention from the list options.
3. Update other methods that modify the content of the editor to also receive focus to the editor to ensure any other intermittencies.
4. Update the isMentionListboxOpened method to read from the hidden property and also wait before reading to resolve the intermittent failures on Firefox when running in loop.

See the discussion below for more details, #2403 (comment)

🧪 Testing

NA

✅ Checklist

• I have updated the project documentation to reflect my changes or determined no changes are needed.

[rajsite]

Should poke at isMentionListboxOpened a bit more