Make Manage Windows scrollable.

Adds the Manage Windows menu root view to a ScrollView that has a max
height of 2 rows. If the menu has more than 2 rows, it will be
scrollable.

Bug: 428203288
Test: Manual; open header and handle manage windows menus with 7+
instances of Drive open.
Flag: com.android.window.flags.enable_desktop_windowing_multi_instance_features

Change-Id: I1153ecd054baf858a16d080b09482a2977e793bc