Use stdint types for FX_WORD and FX_DWORD.
Use stdint types for FX_WORD and FX_DWORD.

This Cl changes the definition of FX_WORD and FX_DWORD to use the stdint
types. This will allow changing the uses on a directory basis to the
stdint types.

R=thestig@chromium.org, tsepez@chromium.org

Review URL: https://codereview.chromium.org/1727203002 .

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium