Built-in Transforms should be used when available

[doug-walker]

In some of the color spaces (e.g. camera logs) the current configs contain individual transform operators even when a Built-in Transform is available.

The benefit of that is that it is more apparent what math is being applied. The drawback is that it is not apparent at a glance whether the matrix coefficients and etc. are really the correct ones for that color space (e.g. a specific camera log) or whether they have been tampered with.

At the working group discussion today, it was felt that it is somewhat preferable to use the Built-in Transforms whenever they exist. This proposal is to update the Python script to insert a Built-in Transform if it exists for the given OCIO version that the config is being built for.