m3: guard wear material3 UI change for AlertDialog

Share the same UX change guarding condition as Platform Button
(ag/30167572):
1. app target sdk is 36 or above.
2. feature flag rolled-out.
3. device is a watch.
4. button uses Theme.DeviceDefault.

Group Wear Material3 styles to a new layout and only refer it
in the new style. This decouple the new from old style hierarchy to
avoid messing up layout if existing AlertDialog has its own style
tweeks.

Bug: 377422490
Bug: 379365266
Test: manual
Flag: android.widget.flags.use_wear_material3_ui
Change-Id: I230b74d5e2b0d2b599f24a01d7548076f45151d1