Reland "[iOS][MF] Fix search in all passwords"

This is a reland of b400d6c7

Original change's description:
> [iOS][MF] Fix search in all passwords
> 
> If the password view controller was presenting something, it will stay
> around. This is fixed and a test is added.
> 
> Bug: 1008421
> Change-Id: I8248cbbf28be94bc4b84c65ccda42129a192db0b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1826895
> Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
> Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#702358}

Bug: 1008421
Change-Id: I04c8b6baa91c87884c6b792cb67fa75cc8faed6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1852284Reviewed-by: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Auto-Submit: Javier Ernesto Flores Robles <javierrobles@chromium.org>
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#704593}

ios/chrome/browser/ui/autofill/manual_fill/all_password_coordinator.mm

@@ -75,8 +75,9 @@
 }
 
 - (void)stop {
-  [self.passwordViewController dismissViewControllerAnimated:YES
-                                                  completion:nil];
+  [self.passwordViewController.presentingViewController
+      dismissViewControllerAnimated:YES
+                         completion:nil];
   self.passwordViewController = nil;
   self.passwordMediator = nil;
   [super stop];