AfformScanner - Use `ang/*.aff.json` file-naming convention

AfformScanner - Use `ang/*.aff.json` file-naming convention

__Before__: Scan each `$extension` for `$extension/afform/*/meta.json`

__After__: Scan each `$extension` for `$extension/ang/*.aff.json`

__Comments__: This is a significant breaking change for v0.2.

It preserves some key design-goals from the old naming convention

* The symbol in HTML (e.g.  `afform-email`) should have symmetry with the file-name (e.g.  `afform/Email/*` or `afform-email.*`)
* The file-name in the base-code provided by an extension should match the file-name in the local override folder.

However, the new naming convention also:

* Makes it easier downstream to choose their own prefixes. We're not boxed-in or hard-coded to `afform-`.
  This will be useful, e.g., with distinguishing the stdlib from the business-forms that use the stdlib.
* Puts Afform-Angular content in the same folder structure as Regular-Angular content.