Update undo snackbar visuals

- Use accent color for action
- Update font-family to use TextTitle style
- Reduce elevation to 3dp
- Inset snackbar left/right margins more, unless we need to increase the
  width to fit the text
- For largest display/font size, fallback to 2 lines and smaller font if
  necessary to not cut off the label
- Remove top/bottom padding on action (b/114084048)
- Allow up to 20 char for the action (b/114317987)

Change-Id: I833c102aaac3ba3db2283997c142926c3830336d