collate: move iter from collate to internal/colltab

This allows it also to be used by the search package to
implement search on non-normalized strings.

Change-Id: I1265bd49ccca2c3fc22a7bb3d4f11f33375c3045
Reviewed-on: https://go-review.googlesource.com/10571
Reviewed-by: Nigel Tao <nigeltao@golang.org>
4 files changed