Fix back arrow sometimes has wrong size on main display

The context returned by context.createWindowContext was used to inflate
the back arrow view. This caused the resources of the view to not be
updated on some configuration updates. This CL uses the default context
for the main display instead which fixes the bug.

Bug: 409384343
Test: Manual, i.e. verified that back arrow does not have different
      size after changing display resolution in settings. Also verified
      that back arrow has correct size on connected display.
Flag: com.android.window.flags.enable_multidisplay_trackpad_back_gesture
Change-Id: I26692885423feabfed34702551fd6b610de3cf3e