This change adds AbstractCode, which can be either Code or
BytecodeArray, and adds methods to calculate source position based
on that. Also cleans up to use code offsets instead of raw PC
where possible, and consistently uses the offset from instruction
start (as opposed to code object start).

R=rmcilroy@chromium.org, vogelheim@chromium.org
BUG=v8:4690
LOG=N

Review URL: https://codereview.chromium.org/1618343002

Cr-Commit-Position: refs/heads/master@{#33579}