Fix invalidation of bound textures/shaders across a renderer flush on D3D9

[cgutman]

Description

The following sequence of renderer commands is currently broken on D3D9:

SDL_RenderTexture(renderer, yuv_texture, NULL, NULL);
SDL_FlushRenderer(renderer);
SDL_RenderTexture(renderer, rgb_texture, NULL, NULL);

The problem is that when SDL_FlushRenderer() calls D3D_InvalidateCachedState(), the renderer forgets that it still has the YUV shader and U/V planes bound. SetDrawState() then thinks it only needs to update texture 0 before rendering. The result is that the area where the RGB texture is supposed to go is instead drawn with the YUV shader with RGB texture as the Y plane and the U/V planes from the last YUV texture.

This PR fixes the issue by adding a new texture_state_dirty member which forces SetDrawState() to update the bound textures and shader. It also fixes the case where an app might have bound their own textures or shader after SDL_FlushRenderer() and not unbound them before calling into SDL again.

Existing Issue(s)

[slouken]

Merged, thanks!