[Shopping Service] Support checking user account in shopping service

This CL adds an AccountChecker to check if user signs in, enables
MSBB, enables web and app activity (WAA), etc. This class is
instantiated in ShoppingService and can be passed into other
components such as subscriptions.

We use a separate build target for account checker and also move
pref names to another separate one to avoid circular dependencies.

For now we just update users' WAA status on identity change and copy
the query parameters from web history service. In long term we should
figure out a better way to query this status.

Bug: 1348672
Change-Id: I61df756a31cb543ee2defe02dc0d190114e64e8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3828716


Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Commit-Queue: Zhiyuan Cai <zhiyuancai@chromium.org>
Reviewed-by: Mihai Sardarescu <msarda@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1041135}