Move pod_array.h and sparse_{array,set}.h from util/ to re2/.

Change-Id: I1dcfbdd4546891108cf25a3397c0aa5cc1c07192
Reviewed-on: https://code-review.googlesource.com/c/re2/+/46510
Reviewed-by: Paul Wankadia <junyer@google.com>
16 files changed