fix(designer): Trigger Body Output Fixes

[Eric-B-Wu]

A couple fixes based on issue: Fixes #4854

1. Instead of using Body as the title in as the default Output body, we'll follow old designer and if there's a description to use that as the output title
2. When we generate the expression from the key, we'll only shift the root segments if there is an actionName. that way something like ["Body", "$", "Body"] won't default to @triggerBody()