Fix final blit in OpenGL when stereo rendering is used

[BastiaanOlij]

Not sure how long this has been broken but stereo rendering with the mobile VR Interface was broken completely.

Couple of things were wrong:

• Incorrect usage of GL_TEXTURE_2D, needs to be GL_TEXTURE_2D_ARRAY when stereo is used
• Texture filtering was not being set correctly causing error spam
• As we're vertically flipped, faces were being culled and we didn't render anything

See godotengine/godot-demo-projects#1212 for a demo project with which to test this.

[clayjohn]

This would have been a fairly recent regression from #106267

[akien-mga]

Thanks!