Request for API to calculate the value of setLogExposureStep

When creating an exposure transform for a logarithmic color space we get the best (most predictable) behavior if we use a an exposure step that reflects the colorspace. The exposure transformation exposes this API: "setLogExposureStep".
However, given an arbitrary color space there is no (easy) way of calculating this value.
We request that an API such as defaultLogExposureStep is exposed on an OCIO color space.

Start by tracing the existing setLogExposureStep exposure-transform API and the OCIO color-space API. Determine what defaultLogExposureStep should mean for an arbitrary color space and how the proposed API should expose it. Done means the behavior and API contract are defined and covered by appropriate tests.

Written by the indexing model from the issue text.