Prevent force showing system bars for TaskView

Update the condition of force showing system bars to check adjacent
tasks instead of checking multi-window windowing mode so it can
distinguish from TaskView.

Bug: 273495037
Test: atest TaskDisplayAreaTests DisplayPolicyTests InsetsPolicyTest
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:2bd0fe76a6b4ef566386e1949e4db0cf0db16430)
Merged-In: I1c51c6f66cd6967651068de1ffc2e6e8566f5a46
Change-Id: I1c51c6f66cd6967651068de1ffc2e6e8566f5a46