Add the exclamation cutout for the stacked mobile icon

This includes a fix to a bug where the width of the bars weren't calculated properly

Test: manually using demo mode
Fixes: 395603295
Flag: com.android.systemui.status_bar_root_modernization
Flag: com.android.settingslib.flags.new_status_bar_icons
Change-Id: Iac5626535b1daccdedfb386072ce109ead47aaff