Media: Store attachment’s file size in metadata.

Store the file size of all newly uploaded attachments, as part of the metadata stored in post meta. Storing file size means, developers will not have to resort to doing `filesize` function calls, that can be time consuming on assets on offloaded to services like Amazon’s S3. 

This change also introduces a new helper function called, `wp_filesize`. This is a wrapper around the `filesize` php function, that adds some helpful filters and ensures the return value is an integer.

Props Cybr, Spacedmonkey, SergeyBiryukov, johnwatkins0, swissspidy, desrosj, joemcgill, azaozz, antpb, adamsilverstein, uday17035. 
Fixes #49412. 



git-svn-id: https://develop.svn.wordpress.org/trunk@52837 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/file.php

@@ -262,4 +262,39 @@ class Tests_File extends WP_UnitTestCase {
 
 		return $keys;
 	}
+
+	/**
+	 * @ticket 49412
+	 * @covers ::wp_filesize
+	 */
+	function test_wp_filesize_with_nonexistent_file() {
+		$file = 'nonexistent/file.jpg';
+		$this->assertEquals( 0, wp_filesize( $file ) );
+	}
+
+	/**
+	 * @ticket 49412
+	 * @covers ::wp_filesize
+	 */
+	function test_wp_filesize() {
+		$file = DIR_TESTDATA . '/images/test-image-upside-down.jpg';
+
+		$this->assertEquals( filesize( $file ), wp_filesize( $file ) );
+
+		$filter = function() {
+			return 999;
+		};
+
+		add_filter( 'wp_filesize', $filter );
+
+		$this->assertEquals( 999, wp_filesize( $file ) );
+
+		$pre_filter = function() {
+			return 111;
+		};
+
+		add_filter( 'pre_wp_filesize', $pre_filter );
+
+		$this->assertEquals( 111, wp_filesize( $file ) );
+	}
 }