Is your feature request related to a problem? Please describe.

When dealing with attachments in the new Posts API , instead of calling new Image() or new Attachment() directly, one would just call Timber::get_post(). This is a potential point of confusion, as in some cases it may not be obvious from looking at user code that we're actually getting an attachment:

<img src="{{ get_post( post.meta('my_img') ) }}">

This is arguably more intuitive:

<img src="{{ get_image( post.meta('my_img') ) }}">
{# or #}
<img src="{{ get_attachment( post.meta('my_img') ) }}">

Describe the solution you’d like

Two small additions to the API:

1. Add Timber::get_image() and Timber::get_attachment() as aliases to Timber::get_post()
2. Add corresponding get_image() and get_attachment() Twig functions

The drawback here is that aliases are also potentially confusing, since it's possible you won't get an Attachment instance back from ::get_attachment(). But this is probably less likely than the inverse case, since you're unlikely to use ::get_attachment() in a situation where you don't already have an attachment ID. To cover out bases, in the docs we should say something like:

Alias for Timber::get_post(). Honors Class Maps and query params in exactly the same way. That means it's possible to get something other than an Attachment (such a plain Timber\Post object) back if you pass something other than an attachment ID. Intended to clarify your code when you already know you have an attachment ID.

Describe alternatives you’ve considered

Just using ::get_post() for everything. Potentially confusing.

Additional context

Discussion starts here: #2316 (review)