Add Post Effect Detection + Attachment Clear Color Skips

[thr3343]

This PR adds two RenderPass related Optimisations:

• Color Clear Skips:
  • This adds code that automatically skips Color Attachment Clears if the color is the same _i..e has already been applied)
  • Help reduce pipeline stalls, which can improve performance by quite alot in some scenarios
• RenderPass Modes
  • Uses crude Post Effect detection to switch between DefaultPass and LegacyPass if a Post effect Shader is active
  • Using DefaultPass Improves performance by Approx 10%+ in default conditions (if no additional shaders are active)