Update colors & text in promoted notification info

This change:
- Updates the demotion text per UXW guidance
- Adds an unpin icon to the "Turn off" button
- Updates the colors to meet a11y requirements, and adds a border

Bug: 412579162
Test: manual
Flag: com.android.systemui.permission_helper_ui_rich_ongoing
Change-Id: I7b52d3b839291fb8b738e8c8bb04db948eee45af