Notification bundle header UI tweaks

 - Resize bundle header view: 48dp
 - Resize bundle icon and add background
 - Resize some padding inside bundle header

Flag: com.android.systemui.notification_bundle_ui

Test: atest BundleHeaderGutsScreenshotTest
Test: atest  BundleHeaderScreenshotTest
Bug: 439043409

Change-Id: I53fb7213b0466a3acc710424724333f8304c6d4f