This CL removes all setters from the Operand and removes the friendship
relation between Assembler and Operand. All data fields of the Operand
are set exactly once in the constructor, the Operand is immutable
afterwards.
In order to construct the data of an Operand easily, the OperandBuilder
is introduced. After building an Operand, the data is copied to the
const field of the Operand.

R=mstarzinger@chromium.org

Bug: v8:7310
Change-Id: I1628052b8a0c47cbfbc3645dfdac5a0e9705977b
Reviewed-on: https://chromium-review.googlesource.com/936741Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51563}