This CL introduces InstanceTypeChecker namespace with type checkers for
types used by the optimizing compiler. The type checkers are global
functions. Examples:

bool InstanceTypeChecker::IsJSFunction(InstanceType);
bool InstanceTypeChecker::IsAllocationSite(InstanceType);

The CL also uses these type checkers in the HeapObject::IsXXXX()
functions to ensure consistency.

Bug: v8:7790
Change-Id: I7eb9e79ca28da02fd489201f532e566d0d13243a
Reviewed-on: https://chromium-review.googlesource.com/1154529Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54782}