Built-in Transforms should be used when available

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.

Locate the Python script that builds the configs and inspect how individual transform operators are selected for each OCIO version. Check Built-in Transform availability for the relevant color spaces and versions; done means generated configs use a Built-in Transform where available and retain the existing operators otherwise.

Written by the indexing model from the issue text.