Clean up some "GetProperty" methods/functions.

Runtime::GetObjectProperty:
  - handled string.charAt, element access and property access
  - now handlified
GetProperty in handles.cc:
  - called to Runtime::GetObjectProperty
  - now removed
Object::GetProperty (handlified version):
  - handled element access and property access
  - now changed to only do property access
New: Object::GetPropertyOrElement:
  - handles element access and property access

R=ishell@chromium.org

Review URL: https://codereview.chromium.org/210953005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20327 ce2b1a6d-e550-0410-aec6-3dcde31c8c00