Separate agg-authored code from fx-authored code.

Creates a separate library so we can apply less-strict warnings to
the code we can't change from upstream vs. the code we can change,
reducing noise in the standalone build.

Remove needless foo.{cpp,h} files that merely perform indirection
via #include "some_other_path/foo.{cpp,h}".

BUG=pdfium:166
R=brucedawson@chromium.org, thestig@chromium.org

Review URL: https://codereview.chromium.org/1152743007.
54 files changed