Fix: Set WebLayerAccessibilityUtil in BottomSheetController

Not setting the WebLayerAccessibilityUtil results in a
NullPointerException when calling `shouldGestureMoveSheet` when the
BottomSheet is not yet opened.
(https://source.chromium.org/chromium/chromium/src/+/main:components/browser_ui/bottomsheet/android/internal/java/src/org/chromium/components/browser_ui/bottomsheet/BottomSheet.java;l=212;drc=0e24535efdfbc5c4adf8f10284e66d50e14a037a?q=BottomShee&ss=chromium%2Fchromium%2Fsrc)

This is analogous to the implementation in Chrome:
https://source.chromium.org/chromium/chromium/src/+/main:chrome/android/java/src/org/chromium/chrome/browser/ui/BottomSheetManager.java;l=138?q=setAccssibilityUtil

Change-Id: I701af36e249982d83a12ab2a2814205f68060fce
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3494704
Reviewed-by: Rayan Kanso <rayankans@chromium.org>
Reviewed-by: Bo Liu <boliu@chromium.org>
Commit-Queue: Susanne Westphal <swestphal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#976261}