Implement FPDFAction_GetFilePath().

The API is the same as the Foxit version, except the encoding is
specified as UTF-8 instead of local encoding.

Also remove CPDF_LWinParam since it's unused.

BUG=chromium:517713
R=jun_fang@foxitsoftware.com

Review URL: https://codereview.chromium.org/1335373002 .
8 files changed