GraphicsBitmap: create_wrapper() should take pitch as a parameter

We shouldn't assume that the pitch of some arbitrary bitmap memory that
we're wrapping is going to be 16-byte aligned. Instead, just take the
pitch as a parameter.

Also update WindowServer to pass the pitch to the framebuffer bitmaps.

Servers/WindowServer/WSScreen.h

@@ -16,6 +16,7 @@ public:
 
     int width() const { return m_width; }
     int height() const { return m_height; }
+    size_t pitch() const { return m_pitch; }
     RGBA32* scanline(int y);
 
     static WSScreen& the();