Fast track all changes to FSE variation

[bacoords]

As part of the migration, this PR fast tracks all of the changes that were made to get the original FSE variation started. For historical reference:

https://github.com/withtangent/tangent/pull/12 https://github.com/withtangent/tangent/pull/11 https://github.com/withtangent/tangent/pull/9 https://github.com/withtangent/tangent/pull/8 https://github.com/withtangent/tangent/pull/7 https://github.com/withtangent/tangent/pull/6 https://github.com/withtangent/tangent/pull/3