Clarify meaning/default for `raw` variable setting

What does this MR do?

Clarifies the meaning of the newish raw field that was introduced with Frontend: Make it possible to set variables as ... (#217309 - closed)

I think the current wording is very misleading. By having Whether the variable is expandable. Default: false so close together, it registers as "It is not expandable by default" when reading. But that is not true, because "raw set to false" means "expandable is true".

I find it somewhat confusing in general that we address this from two different perspectives in the API (Is it raw?) versus the UI (Is it expandable?), but this should at least make the API docs a bit clearer.

Related issues

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