Remove IsBlockTerminator and introduce InstructionScheduler::AddTerminator in
order to handle block terminator instructions.

Instead of the kBlockTerminator flags, we now rely on Instruction::IsTrap(),
Instruction::IsDeoptimizeCall() and explicitly denoting block terminators
when adding them with InstructionScheduler::AddTerminator().

IsBlockTerminator incorrectly included deopts when they were not at the end of
a block, which meant that an instruction with side effects could have been
reordered with respect to a deopt as the deopt was not identified correctly.

Since the snapshot does not contain deopts, this is not causing any problems
at the moment (the scheduler is only enabled on the snapshot).

Change-Id: I1c2dad748a9398a3355630d9a542f4ac89afaa42
Reviewed-on: https://chromium-review.googlesource.com/960501Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georgia Kouveli <georgia.kouveli@arm.com>
Cr-Commit-Position: refs/heads/master@{#52019}