Modal bottom sheet matches screen width by default

Specifying android:minWidth on bottom sheet prevents its child from
matching the parent's width. If I simply remove it, the modal bottom
sheet is always as wide as its content, and there's no way for the
client app to make the bottom sheet match the screen width.  Instead,
this makes the modal bottom sheet match the screen width. The client app
can still make the bottom sheet narrower by specifying
layout_marginLeft/Right.

Bug: 26761954
Change-Id: Ic0cb1f39dcf3c2e3119eef0c369397a483691f49
2 files changed