[PWA/Nav capturing] Fix crash with focus-existing PWAs from intent icon

Currently, the link capturing flow for reparenting an app by clicking
on the intent picker icon will crash Chrome if the app has a launch
handler of focus-existing or navigate-existing. This is because of an
UAF in the WebAppsIntentPickerDelegate triggered by the reparenting
logic which handles these launch handlers separately by destroying
the old web contents [1].

Destruction of web contents destroys the IntentPickerTabHelper which
owns the delegate, which means WebAppsIntentPickerDelegate::LaunchApp()
crashes while trying to reference any class variables.

This CL fixes that by creating an overload of the reparenting function
that takes in a callback, and runs it with the web contents that
are created as part of the reparent flow. By doing so, the final
resultant web contents are always used to perform logic in, and if
things needed to be done with it, that can happen inside a callback.

The reparenting call cannot itself be asynchronous, because it is
triggered from the menu model under the IDC_OPEN_IN_PWA_WINDOW
command. That has been maintained with the current implementation.

[1] https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/web_applications/web_app_launch_utils.cc;l=440;drc=451093bbaf7fe812bf67d27d760f3bb64c92830b;bpv=1;bpt=1

Bug: 359224477, 356165283
Change-Id: If417433fd076a8f739adcd05e576c8931dd885c8
Include-Ci-Only-Tests: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5862344
Commit-Queue: Dibyajyoti Pal <dibyapal@chromium.org>
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1356199}