Add support to log source position offsets to the profiler. As part of
this change PositionsRecorder is split into two, with the subset needed
by log.cc moved into log.h and the remainder kept in assembler.h as
AssemblerPositionsRecorder. The interpreter's source position table
builder is updated to log positions when the profiler is active.

BUG=v8:4766
LOG=N

Review URL: https://codereview.chromium.org/1737043002

Cr-Commit-Position: refs/heads/master@{#34416}