[analyzer] Model trivial copy/move ctors with an aggregate bind.

This is faster for the analyzer to process than inlining the constructor
and performing a member-wise copy, and it also solves the problem of
warning when a partially-initialized POD struct is copied.

Before:
  CGPoint p;
  p.x = 0;
  CGPoint p2 = p; <-- assigned value is garbage or undefined

After:
  CGPoint p;
  p.x = 0;
  CGPoint p2 = p; // no-warning

This matches our behavior in C, where we don't see a field-by-field copy.

<rdar://problem/12305288>