This CL surfaces AssemblerOptions to CodeAssembler::GenerateCode and
to pipeline methods. To allow forward declaring AssemblerOptions,
AssemblerBase::Options was moved out of the AssemblerBase class.

Bug: v8:6666
Change-Id: If9fc50d3d4767bb5dd39a0c3b6e094021f4cae2b
Reviewed-on: https://chromium-review.googlesource.com/1127039
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54286}