shaders/colorspace: scale down saturation when raising brightness

Avoids excessively over-saturating when tone mapping upwards in brightness, which generally leads to an unnatural effect. Tested with both black point compensation and inverse tone mapping.

Fixes: #280 (closed)

changed milestone to %v6.283+

mentioned in issue #280 (closed)

approved this merge request

added 4 commits

• 701905b2...fea66198 - 3 commits from branch videolan:master
• f06efc75 - shaders/colorspace: scale down saturation when raising brightness

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merged