File template feature for VSCode

Description

The current Web IDE and the Web Editor (single file editor) offer a "file template" feature that applies a pre-set template to a (ideally new) file. As we transition the Web IDE to use VS Code, we need to consider how that feature will work in the context of the new editor.

Existing options

Challenges

1. VS Code offers less when it comes to customization of the UI. We may have to get creative for where this feature goes.
2. As discussed in #300286 (closed) and !18337 (comment 615017545), the results from the API are returned ungrouped, which is inconsistent with the repository view / single file editor.