[Cocoa] Add file filter menu to create_file_dialog
[Cocoa] Add file filter menu to create_file_dialog

This makes choosing between multiple file filters similar to that on
other platforms.

r0x0r/pywebview,shivaprsdv/pywebview,shivaprsdv/pywebview,r0x0r/pywebview,shivaprsdv/pywebview,shivaprsdv/pywebview,r0x0r/pywebview,r0x0r/pywebview,r0x0r/pywebview