Move wtf/vector*.* to "blink" namespace

This CL adds WTF:: aliases of vector.h, and blink:: aliases of other
WTF symbols in order to minimize the CL size.

* Add a forward declaration of WTF::Deque to wtf/forward.h
  vector.h needs the Deque declaration.  deque.h includes forward.h to
  verify the correctness of the declaration.

* swap() in vector.h
  It seems the function was not used. Since this CL, the swap()
  belongs to "blink" namespace, and swap() for blink::HeapVector
  matches to this swap().  This CL fixes a build error by replacing
  Swap() with swap().

Bug: 422768753
Change-Id: I57138c7016c946d993f606733e082fbd0ac651a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6733926
Reviewed-by: Koji Ishii <kojii@chromium.org>
Auto-Submit: Kent Tamura <tkent@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1486761}
NOKEYCHECK=True
GitOrigin-RevId: ab09b0113971f395b85035cebc42b8df2438df05