Focus states for keyboard settings button in shortcut helper

+ adjusted paddings for keyboard settings button to avoid focus states
  clipping

Bug: 352305030
Test: Manual - open shortcut helper, using tab + arrow keys navigate to
keyboard settings at the bottom of the left panel, ensure the focus
outline appears around the keyboard settings button.
Flag: com.android.systemui.keyboard_shortcut_helper_rewrite

Change-Id: I57f16d234aa02753789d228289d921e9fa232531