Add CodeItemDebugInfoAccessor

Use it in places where DecodeDebugPositionInfo is called.

Motivation: Abstract away calls to GetDebugInfoOffset.

Bug: 63756964
Test: test-art-host
Test: art/tools/run-jdwp-tests.sh '--mode=host' --debug

Change-Id: I3ab2eff56c472cc717f49d17fd17eb0b8fde4062
14 files changed