New button style for Magic Actions

Adds a new drawable and button style for smart actions coming from the
assistant with a specific extra key.

Actual drawable implementation will land on follow-up CL.

Bug: 383567383
Test: atest SmartActionScreenshotTest
Flag: com.android.systemui.notification_magic_actions_treatment
Change-Id: I0ad7e4751df4885a202c9fbdb5663b589a6e81ef