Reduce shader permutations on iOS

Add option to compile iOS OpenGL ES or Metal shaders and whether to force 32bppHDR at each QL

If Metal shaders are a scalability option we can compile them only for high and compile only OpenGL for low.

For iOS we only really needed Mosaic for iPhone 4 which we no longer (offically) support. All devices we support have FP16.

We can support Encoding or Mosaic as render quality option for iOS because all devices including iPhone 4 do support GL_EXT_shader_framebuffer_fetch. That will bring back iPhone 4 support.

Should reduce the overall number of shaders.