[analyzer] Better model for copying of array fields in implicit copy ctors.

- Find the correct region to represent the first array element when
  constructing a CXXConstructorCall.
- If the array is trivial, model the copy with a primitive load/store.
- Don't warn about the "uninitialized" subscript in the AST -- we don't use
  the helper variable that Sema provides.

<rdar://problem/13091608>

llvm-svn: 178602