Add ability to easily get path to sized images (such as parameter to get_attached_file() or wp_get_attachment_thumb_file())

[paulschreiber]

Currently, you can call get_attached_file() and get the path to the full-sized version of the image.

However, if you want the path to a smaller variant of the image, you end up with something like this:

<?php
$imagedata = wp_get_attachment_metadata( $image_id );
$file_path = get_attached_file( $image_id );
$thumbnail_file = str_replace( wp_basename( $file_path ), $imagedata['sizes'][ $size ]['file'], $file_path );

Or like this:

<?php
$imagedata = image_get_intermediate_size( $image_id, $size );
$upload_directory = wp_get_upload_dir();
$thumbnail_file = $upload_directory['basedir'] . '/' . $imagedata['path'];

For brevity, these examples omit the null dereference checks, which triple the size of the code needed.

This is similar to the behaviour of wp_get_attachment_thumb_file(), but that function hard-codes thumb as the only size.

It would be very helpful if this existed:

<?php
get_attached_file( int $attachment_id, bool $unfiltered = false, string $size = false )

Or this existed:

<?php
wp_get_attachment_thumb_file( int $post_id, string $size = false )

See related tickets #33959 (from 2015) and #17262 (from 2011).

I'm happy to make a patch for either/both of these approaches, but don't know which one you prefer, and don't want this to languish for 11 years.