Snippets: support default values without editor support

[FireChickenProductivity]

The current community approach is to just insert the default value without editor support, which means you cannot even treat it like a stop.

[nriley]

A potential way to move forward:

• Don't automatically replace the default value in the snippet stop
• Instead, display a notification indicating that a default value is available and mentioning the voice command that will insert the default value at the insertion point.