HeapObject::SizeFromMap() was too large to get inlined anyway.
HeapObject::IsFoo() predicates should be implemented in foo-inl.h,
because that's what they depend on.
This patch also fixes up includes: dropping unnecessary ones from
object-inl.h, and adding them in other places that previously
relied on getting them transitively.

Bug: v8:8562
Change-Id: Id062bed67257d9dc1899f2d71f44cf69a1368c83
Reviewed-on: https://chromium-review.googlesource.com/c/1450778Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59478}