Support x:document inside x:option

[bertfrees]

for options that are annotated with px:type="anyFileURI" in the Pipeline.

Instead of

<x:option name="tts-config" select="resolve-uri('../resources/tts-config.xml')"/>

you would be able to do

<x:option name="tts-config">
   <x:document type="inline">
      <config>
         <property key="..." value=""/>
      </config>
   </x:document>
</x:option>

In addition, if x:document (or x:data?) would support non-XML data, instead of

<x:option name="stylesheet" select="resolve-uri('../resources/braille.scss')"/>

you could do

<x:option name="stylesheet">
   <x:document type="file" select="../resources/braille.css"/>
</x:option>