This patch adds parsing of spread object property.

-- Changes ParsePropertyName to parse Token::ELLIPSIS.
-- Throws if rest is encountered by setting a pattern error.
-- Adds a new PropertyKind enum (SPREAD)
-- Adds a new ObjectLiteralProperty::kind (SPREAD)
-- Adds a new harmony-object-spread flag and protects the parser code
with it.
-- Adds a new runtime function called CopyDataProperties
-- Does not add any support for this feature in fullcodegen.
-- Ignition calls out to a runtime function CopyDataProperties to
perform spread operation.
-- Move FastAssign from builtins-objects.cc to objects.cc
-- Refactor Builtin_ObjectAssign to use SetOrCopyDataProperties

Object rest will be implemented in a follow on patch.

BUG=v8:5549

Review-Url: https://codereview.chromium.org/2606833002
Cr-Commit-Position: refs/heads/master@{#42102}