Fix the horizontal margins on the left panel in the two pane picker.

The recycler view when displayed in single pane picker, for large screen
gets a larger padding. But when displayed in two pane picker, it is not
needed - so we override it.

Foldable's unfolded portrait doesn't seem to have screenshot test
- will look into if we can add one in follow up.

Bug: 322719955
Test: Screenshot test for existing modes & manual (see bug)
Flag: ACONFIG com.android.launcher3.enable_unfolded_two_pane_picker DEVELOPMENT

Change-Id: Ibd72146e7e5230eec0d2ce01c3917819a73d8f32