feat(expressive): Update Display size & text reset & preview

- Replaces custom Reset preference with a standard SettingsLib
  ButtonPreference
- Tags the Preview preference as already having rounded corners

Fix: 403312690
Bug: 399173131
Flag: EXEMPT largely refactoring, low risk
Test: atest com.android.settings.accessibility
Test: Use preference manually, tapping & with TalkBack
Test: Observe new UI; see screenshots in bug
Change-Id: I6caf4ca194359232cd94ef7efc34c72ee94475cf