Adds Gamepad API.

Gamepad API in libwpe is middleware between WPEWebKit and the application,
such as cog.

The application is reponsible to provide the gamepad backend by offering
the functions for providers and gamepads.

WPEWebkit shall provide event callbacks.

Original patch by Eugene Mutavchi <[email protected]>

Author: ceyusa

CMakeLists.txt

@@ -62,6 +62,7 @@ set(WPE_PUBLIC_HEADERS
     include/wpe/version.h
     include/wpe/version-deprecated.h
     include/wpe/export.h
+    include/wpe/gamepad.h
     include/wpe/input.h
     include/wpe/input-xkb.h
     include/wpe/keysyms.h
@@ -85,6 +86,7 @@ add_library(
     src/renderer-host.c
     src/version.c
     src/view-backend.c
+    src/gamepad.c
 )
 
 if (BUILD_SHARED_LIBS)