Refactor GetEffectiveClientModeAndBrowserForCapturing

This splits up the old GetAppHostForCapturing helper method
into 3 separate methods for the various bits of functionality
it was used for:
- AppBrowserController::FindNoOpenerTabForWebApp, to find an existing
  tab to navigate or focus for a navigate or focus existing launch mode.
- A helper FindNormalBrowser method that returns the most recently
  active "normal" browser in a given profile.
- A bug fix for the existing AppBrowserController::FindForWebApp
  method, to return the most recently active non-popup app browser
  for a given app id.

These 3 pieces are then combined back together in a new
GetEffectiveClientModeAndBrowser method now as part of the
NavigationCapturingProcess class. This does mean that in some
cases we're iterating over all the browsers multiple times
(first to see if there is a tab to capture a focus/navigate existing
navigation, and if there was none a second one to figure out what
browser to open the new tab in), I think this makes the code more
readable and easier to extend to add support for tabbed mode.

Finally, the other place where the old GetEffectiveClientMode
method was used, in the intent-picker focus/navigate existing code,
we call FindNoOpenerTabForWebApp directly, as we're always in the
same branch of the old method in this case.

Bug: 390257745
Change-Id: I64bd3d7f9a1a9a7e687e3c533dd5e3cee58d0ada
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6213068
Reviewed-by: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1414285}