Update two pane sheet widget picker to use RelativeLayout since ConstraintLayout was causing test failures

There are test failures when using ConstraintLayout without a known solution, see https://chat.google.com/room/AAAACwktJi8/2OogGWfbLvI. Switching back to a relativelayout to resolve those issues.

Bug: 301918659
Test: WidgetPickerImageTest
Flag: ACONFIG com.android.launcher3.enable_unfolded_two_pane_picker DEVELOPMENT
Change-Id: I004c2d77ca308d85b29217d4f1e548067126556f
3 files changed