Add serialization prefs when opening, downloading XML documents from database

[joewiz]

Before this PR eXide hard-coded serialization parameters—indent=yes expand-xincludes=no when opening and downloading XML documents from the database and indent=no expand-xincludes=no when generating and downloading packages—and users had no means to change this behavior. Numerous times the indentation behavior of eXide caused confusion when users opened documents or saved documents and observed whitespace introduced into their documents. See these posts to exist-open:

• eXide expands XIncludes when opening XML files (2012)
• How to prevent indenting with eXide / eXist ? (2017)
• how can indentation of element-only nodes be suppressed? (2020)

The only solution was to suggest editing eXide's sources to change the hardcoded default or to use a different editor.

This PR adds preferences for these two serialization parameters to the eXide preferences window:

The preferences default to the longstanding eXide defaults for opening and downloading individual documents: indent=yes expand-xincludes=no. The preferences also now govern serialization when generating and downloading packages via Application > Download app, and thus the default here is changed from a hardcoded indent=no to follow the eXide Preference.

The load.xql endpoint now supports indent and expand-xincludes parameters, just as deployment.xql had already done.

Alternatives I considered:

• Showing these preferences in the editor window. I opted to place these options in Preferences since in the main editor window, they would take up valuable space; there's no good place for this in the UI; the "indent on load" checkbox could cause confusion with the "indent" checkbox in the results pane; and we've never had the ability to adjust this before, so it's doubtful we'd want/need to toggle this all of the time. Let's give this a try and see if we really need to toggle this on .
• Providing distinct preferences for (a) opening/downloading individual documents vs. (b) generating & downloading packages. I opted for a single set of preferences for simplicity's sake; it seems to me that if you like indentation, you'd want it everywhere, but if you don't want indentation, you'll disable it and want to keep it off.
• Setting the defaults via eXide's configuration.xml file instead of src/preferences.js - but none of the other preferences are set there, and I am not capable of the javascript needed to get the preferences.js file to read eXide's prefs from the configuration.xml file.

Previous work in this area includes:

• set expand-xincludes=no when downloading app xar #158
• Add an indent parameter to the download xar endpoint #272

[joewiz]

@adamretter Thank you!

[adamretter]

@joewiz you are very welcome. I have also assigned @younes to take care of eXist-db/exist#2394 for you