gn_to_bp.py fixes

  - no u"" strings
  - more pervasive sorting
  - include sources from optional Skia components (e.g. gpu, codec, pdf)
  - cosmetic nits

Change-Id: Ief0f293117dbfbc97584db185c067a8297067b74
Reviewed-on: https://skia-review.googlesource.com/5643
Reviewed-by: Leon Scroggins <scroggo@google.com>
1 file changed