Make 'populate file from snippet' command more discoverable

[ulugbekna]

• Show the command in ghost text in the empty file, ie another option along with "select language" and "open a different editor"

Fixed in #173128

• Explore whether we also want to be able to create a new file with a snippet, ie context menu : File > New File... > [Quick pick option to create from snippet] --
  UPD: In my opinion, this disrupts the current idea of the quick pick which offers different editors, ie creating a file from snippet would be a completely different option from the rest. I propose that we wait for a feature request to come in before investing time to implement this.

[jrieken]

fyi @digitarald

[ulugbekna]

How to verify:

1. Open a new file (cmd + n) - you should see ghost text with various options, one of which is fill with template
2. fill with template should open a quick pick with various snippets - both picking a quick pick item and not picking one should bring focus back to the editor