[dpwa] Generate new test for launch_file_expect[_no]_dialog for Win and
Linux.

1. Update the text_handler and image_handler to foo_handler and
   bar_handler to match the FileHandler basic.json.

2. Change LaunchFileExpect[No]Dialog() to use
   SetStartupDoneCallbackForTesting() instead of checking if a
   browser/tab is opened because opening some files at the same time
   can result in multiple browsers/tabs.


Bug: 1349953
Change-Id: I973192ec4c3de24543c47d1586580b42673941d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4036423
Commit-Queue: Clifford Cheng <cliffordcheng@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1075353}