Media: Relocate wp_filesize() function for use in frontend and backend.

A new function `wp_filesize()` was added with [52837]. The function lived in the `wp-admin/includes/file.php` file. However, this admin specific function is not loaded into memory when hitting `media/edit` endpoint. The result was a `500` Internal Server Error. Why? The function is invoked with that endpoint, but the function does not exist in memory.

This commit relocates the new function to the `wp-includes/functions.php` file. In doing so, the function is available for both the frontend and backend.

Follow-up to [52837].

Props talldanwp, spacedmonkey, costdev, antonvlasenko.
Fixes #55367.

git-svn-id: https://develop.svn.wordpress.org/trunk@52932 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/functions.php

@@ -3458,6 +3458,44 @@ function wp_get_ext_types() {
 	);
 }
 
+/**
+ * Wrapper for PHP filesize with filters and casting the result as an integer.
+ *
+ * @since 6.0.0
+ *
+ * @link https://www.php.net/manual/en/function.filesize.php
+ *
+ * @param string $path Path to the file.
+ * @return int The size of the file in bytes, or 0 in the event of an error.
+ */
+function wp_filesize( $path ) {
+	/**
+	 * Filters the result of wp_filesize before the PHP function is run.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @param null|int $size The unfiltered value. Returning an int from the callback bypasses the filesize call.
+	 * @param string   $path Path to the file.
+	 */
+	$size = apply_filters( 'pre_wp_filesize', null, $path );
+
+	if ( is_int( $size ) ) {
+		return $size;
+	}
+
+	$size = (int) @filesize( $path );
+
+	/**
+	 * Filters the size of the file.
+	 *
+	 * @since 6.0.0
+	 *
+	 * @param int    $size The result of PHP filesize on the file.
+	 * @param string $path Path to the file.
+	 */
+	return (int) apply_filters( 'wp_filesize', $size, $path );
+}
+
 /**
  * Retrieve list of allowed mime types and file extensions.
  *