[iOS] Fix ipad extra vertical space

This patch makes sure the extra space on iPad goes at the bottom of
the view instead of the top.
There is no changes on iPhone.

This also fix a small issue on constraint. The bottom of the scroll
view should be attached to the top of the separator (the one that is
just above the button).

This patch needs to be merge into M124.

Before:
https://drive.google.com/file/d/1Qj5tL14SlxPe7JHVpnyXVVGfyKKA8n4Q/view?resourcekey=0-3f86qDsn2XQwZlYjURMnVQ
After:
https://drive.google.com/file/d/1oOu7n7-MXDvsxv4NJg4ZjgfkbfYjVquR/view?resourcekey=0-NP-f-bJY_RhD3yslI92V-Q


Fixed: 330713313
Change-Id: Iaca0fd933c676c8f18529931ad6e81930d17fb89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5383437
Commit-Queue: Samar Chehade-Lepleux <samarchehade@google.com>
Auto-Submit: Jérôme Lebel <jlebel@chromium.org>
Reviewed-by: Samar Chehade-Lepleux <samarchehade@google.com>
Commit-Queue: Jérôme Lebel <jlebel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1276304}

ios/chrome/browser/ui/search_engine_choice/search_engine_choice_view_controller.mm

@@ -233,8 +233,7 @@ - (void)viewDidLoad {
         constraintEqualToAnchor:self.view.safeAreaLayoutGuide.topAnchor],
     [_scrollView.widthAnchor
         constraintEqualToAnchor:self.view.safeAreaLayoutGuide.widthAnchor],
-    [_scrollView.bottomAnchor
-        constraintEqualToAnchor:_separatorView.bottomAnchor],
+    [_scrollView.bottomAnchor constraintEqualToAnchor:_separatorView.topAnchor],
 
     // Scroll content view constraints.
     [_scrollContentView.topAnchor
@@ -271,8 +270,8 @@ - (void)viewDidLoad {
     [_searchEngineStackView.topAnchor
         constraintEqualToAnchor:_subtitleTextView.bottomAnchor],
     [_searchEngineStackView.bottomAnchor
-        constraintEqualToAnchor:_scrollContentView.bottomAnchor
-                       constant:-kStackViewMargin],
+        constraintLessThanOrEqualToAnchor:_scrollContentView.bottomAnchor
+                                 constant:-kStackViewMargin],
     [_searchEngineStackView.leadingAnchor
         constraintEqualToAnchor:_scrollContentView.leadingAnchor
                        constant:kStackViewMargin],