wined3d: Release the context before potentially destroying the swapchain in wined3d_device_uninit_3d() (Valgrind).

Also try to avoid unnecessary HeapReAlloc() + vsnprintf() loops when we
know the required size of the buffer.

Also rename the shader_buffer_(clear|init|free) functions.

The flag is currently unused and also unnecessary since both
ARB_vertex_shader and ARB_fragment_shader specs require
ARB_shader_objects support.

It's not supported on core profiles and I doubt it matters anyway.
For the records, the default value is 1 so this was actually lowering
the priority for DEFAULT pool textures.