Constrain bc_smartspace_view width with ConstraintSet.MATCH_CONSTRAINT.

In the layout xml, bc_smartspace_view width is configured with
layout_width="match_parent", which doesn't work well with
ConstraintLayout. Looks like this is the root cause for b/362436624.

Flag: EXEMPT bugfix
Fix: 362436624
Test: On Tangor, create a calendar event with a very long title; try rotating lockscreen.
Change-Id: I24ef16b39f83bb48cbe813c6479bf80f402d5a15