Set CanActivate for preview bubble to false.

This prevents the preview bubble from stealing focus from the
Picker widget.

This is better than ShowInactive() because it works even if
someone calls Show() accidentally, as per [1], [2]

[1] https://source.chromium.org/chromium/chromium/src/+/main:chrome/browser/ui/views/tabs/tab_hover_card_bubble_view.cc;l=373;drc=6cdbb075e42a55d812095655d0ac0d06487088b7
[2] https://source.chromium.org/chromium/chromium/src/+/main:ui/views/bubble/info_bubble.cc;l=61;drc=f0b789e57981ab279d092fefb2857f80af9f4f02

Bug: b/330794217
Change-Id: I3deac59beb7e8886aea6cd0e11275e3c3ae74193
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5387145


Auto-Submit: Darren Shen <shend@chromium.org>
Reviewed-by: Michelle Chen <michellegc@google.com>
Commit-Queue: Michelle Chen <michellegc@google.com>
Commit-Queue: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1277418}