Update plugin builder's guide to include inline arithmetic, mapping etc

[jmcook1186]

What
We have added some features to IF recently that required us to update the source code for our builtins. Plugins also need to be updated to support these features. We need to update our plugin buidler's guide to explain the process for supporting these features in new plugins.

Why
To make the plugin building process as easy as possible.

Context
Part of the developer experience upgrades.

Prerequisites/resources
n/a

SoW (scope of work)

• documentation updated to cover all plugin code needed to support latest IF features