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DrawManager: Color Management

The draw manager used to determine if the view transform should be
applied by checking if the scene was not rendered to an offscreen image.

As the sequencer and texture painting needs to render to an offscreen
image with the view transform applied we need to separate the
`do_color_management` from the `is_image_render`.

Reviewed By: fclem

Maniphest Tasks: T64849

Differential Revision: https://developer.blender.org/D4909