Add preference to prefer self-closing tags when tab completing

When tab-completing a new tag, say Thing, it is accompanied by a closing tag like so:

<Thing></Thing>

I work on a project that uses XML files with lots of parameters specified in self-closing tags like so:

<Thing param1="foo" param2="bar" />

it would be helpful if there was a setting to prefer self-closing tags over a separate closing tag or a separate key stroke to insert one or the other (e.g. shift+tab for self-closing).

Start by locating the VS Code XML extension's tab-completion path and checking how existing user preferences are defined. Implement a preference or alternate keystroke for choosing self-closing tags, and verify that tab completion produces the requested XML form without regressing separate closing tags.