vsplit: move kVerticalSnap flag from ash to chromeos

- Rename the command line flag from |ash::features::kVerticalSnapState|
to |chromeos::wm::features::kVerticalSnap|.
- Add chromeos/ui/wm/features.h|cc to support LaCros.

Bug: 1253724
Test: Manual and run affecting unit tests
Change-Id: I0da6ee43e5c889f23f0a265407db90ad876143b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3189770
Commit-Queue: Cattalyya Nuengsigkapian <[email protected]>
Reviewed-by: Ahmed Fakhry <[email protected]>
Reviewed-by: Kyle Horimoto <[email protected]>
Reviewed-by: Sammie Quon <[email protected]>
Cr-Commit-Position: refs/heads/main@{#926501}
diff --git a/chrome/browser/BUILD.gn b/chrome/browser/BUILD.gn
index 3887976..571c979 100644
--- a/chrome/browser/BUILD.gn
+++ b/chrome/browser/BUILD.gn
@@ -5055,7 +5055,6 @@
       "//chromeos/crosapi/mojom",
       "//chromeos/lacros",
       "//chromeos/ui/frame",
-      "//chromeos/ui/wm",
       "//ui/platform_window",
     ]
   }
@@ -5093,6 +5092,7 @@
       "//chromeos/crosapi/cpp",
       "//chromeos/crosapi/mojom",
       "//chromeos/dbus/constants",
+      "//chromeos/ui/wm",
     ]
   }