[PWA] WebAppLinkCapturingBrowserTest running v2, install reparenting fix

This patch:
- updates the WebAppLinkCapturingBrowserTest to run the v2 version for
  non-CrOS.
- Fixes WebAppScopeExtensionsBrowserTests and any test that installs
  a page with `navigate-existing` or `focus-existing`, as the install
  process always reparents, which will find the current tab.

Bug: 377545086
Change-Id: Ibed21edf06628e83ec4f598a5f0037ed12ccba84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5995311
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Auto-Submit: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Daniel Murphy <dmurph@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1379939}