Make CPDFXFA_App / IXFA_AppProvider saner

Move interface comments from the implementation header to the
interface header.

Replace Create / Release functions with static methods.

Replace dubious Release() methods with deletion via virtual dtor, also
for IXFA_App and IXFA_FontMgr while we're at it.

Untabify and fix (theoretically) illegal _CAP include guard definitions
for fpdfxfa/ headers.

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1153553003
15 files changed