Improve tests for MultipleFileUpload

從 MultipleFileUpload 元件及其現有的 snapshot 測試開始。檢視第三方函式庫的 onFileDrop 行為目前如何表示，然後針對回傳的 File 路徑，以及它與單一檔案上傳之間的差異，新增聚焦的涵蓋範圍。完成的標準是相關行為已受到測試，而不只是由 snapshots 涵蓋。

Describe the enhancement or change
Consumer reported the following:

Not really an issue, but I am puzzled by the slight behaviour change of the MultipleFileUpload component.
The onFileDrop callback sends an array of File objects, with properties like path. But it seems this propetrty
changed a little bit:
In PF5 I was getting for example: path: "image.png"
In PF6 I am getting: path: "./image.png"
That's not much of a change and is almost the same in a filesystem. But as I was using this info for the path of the object I am sending into Object Storage, it messed up my app a little bit.
Again, not an issue, I will handle it in my code, but I was wondering if there was a specific reason for this behaviour change? Which does not happen for single file upload btw, it's the plain name of the file only.

We use a third-party library for this piece of the component - we did bump from 14.2.3 to 14.3.5 between versions, so it's possible they changed the file name handling between versions. I don't see a big difference in our code. I do see that we have mostly snapshot tests for this component and do not test the third-party library functionality at all in our tests, so we wouldn't have caught this when we bumped the dependency. We could stand to improve our tests for this component in my opinion.

Is this request originating from a Red Hat product team? If so, which ones and is there any sort of deadline for this enhancement?
No - not blocking.

Jira Issue: PF-1855