Merge to XFA: 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=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1335373002 .

(cherry picked from commit 0b3c8f742613da294f812e2f6e908f4026499f96)
(cherry picked from commit a9d4bc541179ec0436adc4b2e18b7fdecc5952dc)
(cherry picked from commit 4ffd89ed556e32a6527d0e88952fe20ec1e2f362)

Review URL: https://codereview.chromium.org/1345953002 .
8 files changed