d3d8: Use the wined3d declaration to retrieve the d3d8 shader in IDirect3DDevice8Impl_GetVertexShader().

This makes it no longer necessary to create a wined3d vertex shader
when the d3d8 vertex shader has a NULL function.

There is no reason for the rich text format parser to need a handle to
the window, and even if there were it has a handle to the editor which
contains a handle to the window.  It is better to remove this
considering we need to cut down on the use of window handles to
implement windowless richedit controls.

The vertical scrollbar state is stored internally within the control,
so should be used when possible.  This will become more necessary when
windowless richedit controls are implemented, and there will no hWnd
to pass to GetScrollInfo.

Comparing the editor as apposed to the handle to the window will work
just as well right now, but will also work when there is no window
handle to make a comparison with, which will be the case with
windowless richedit controls.

The code for the ME_EnsureVisible function does exactly what
EM_SCROLLCARET does, yet this code is duplicated in order to handle
this message.  It is simpler to just use the existing function to
implement the message, and avoid internally sending the EM_SCROLLCARET
when this function is available.