Postprocessingstack/k upgrade

[kaychang-unity]

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Purpose of this PR

These are various optimisations for the post-processing-stack.
They improve the GPU performance, quality and usability of the post processing effects.
The outputs of the post-processing effects are different and so are not backward compatible.

This is a pet-project for personal use.

Depth-of-Field

• Dynamic selection of number of samples.
  This makes the performance of the effect depending on the number of blur on screen.
  Performance improved by 40% on typical scenes.
• Shader code optimisation.
  Moved some calculations inside the loop generating the bokeh samples as uniform.; moved some temp variables to half; replaced some divisions by multiplications: 7% improvement.
• Manual unrolling of the loop generating the bokeh samples: 15% improvement
• TODO: kernel size parameters is resolution-independent and support up to 4k screen resolution (8 kokeh rings)
• TODO: remove margin code (further improve performance, fix small bokeh denial)
• TODO: Change ring sampling pattern
• TODO: Change color accumulation formula
• TODO: improve sharpness for in-focus pixels and avoid bleeding toward out-of-focus pixels
• TODO: add tilt-shift
• TODO: add bokeh shapes (blade count)

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Testing status

TODO

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Comments to reviewers