Support XML / wrapped export of source

We need to support legacy, wrapped XML format export for all document types, although we'll only default to it for "user types" (e.g., DFI, HL7, LUT, ESD, ...)

This will be subject to a flag in settings that will be initialized on a new instance as being XML-formatted. In a package manager context, the XML/wrapped vs. UDL/unwrapped format will be derived from the description of resources in the package.

Original request: "Export lookup documents in xml format"
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Currently it exports in .lut, which looks like:
```

val1
val2
val3

```

But this format is not importable by $System.OBJ.LoadDir()

Let it be imported as XML documents? as:
```

val1
val2
val3

```