Add database storage for a dedicated file attachment table

Summary: Ref T13603. Prepare to move this relationship out of edge storage into dedicated storage so it is easier to formalize better in the UI.

Test Plan: Ran `bin/storage upgrade`.

Subscribers: PHID-OPKG-gm6ozazyms6q6i22gyam

Maniphest Tasks: T13603

Differential Revision: https://secure.phabricator.com/D21813

resources/sql/autopatches/20220510.file.01.attach.sql

···
+CREATE TABLE {$NAMESPACE}_file.file_attachment (
+  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  objectPHID VARBINARY(64) NOT NULL,
+  filePHID VARBINARY(64) NOT NULL,
+  attacherPHID VARBINARY(64),
+  attachmentMode VARCHAR(32) NOT NULL COLLATE {$COLLATE_TEXT},
+  dateCreated INT UNSIGNED NOT NULL,
+  dateModified INT UNSIGNED NOT NULL
+) ENGINE=InnoDB, COLLATE {$COLLATE_TEXT};

src/__phutil_library_map__.php

···
     'PhabricatorFile' => 'applications/files/storage/PhabricatorFile.php',
     'PhabricatorFileAES256StorageFormat' => 'applications/files/format/PhabricatorFileAES256StorageFormat.php',
     'PhabricatorFileAltTextTransaction' => 'applications/files/xaction/PhabricatorFileAltTextTransaction.php',
+    'PhabricatorFileAttachment' => 'applications/files/storage/PhabricatorFileAttachment.php',
     'PhabricatorFileBundleLoader' => 'applications/files/query/PhabricatorFileBundleLoader.php',
     'PhabricatorFileChunk' => 'applications/files/storage/PhabricatorFileChunk.php',
     'PhabricatorFileChunkIterator' => 'applications/files/engine/PhabricatorFileChunkIterator.php',
···
     ),
     'PhabricatorFileAES256StorageFormat' => 'PhabricatorFileStorageFormat',
     'PhabricatorFileAltTextTransaction' => 'PhabricatorFileTransactionType',
+    'PhabricatorFileAttachment' => 'PhabricatorFileDAO',
     'PhabricatorFileBundleLoader' => 'Phobject',
     'PhabricatorFileChunk' => array(
       'PhabricatorFileDAO',

src/applications/files/storage/PhabricatorFileAttachment.php

···
+<?php
+
+final class PhabricatorFileAttachment
+  extends PhabricatorFileDAO {
+
+  protected $objectPHID;
+  protected $filePHID;
+  protected $attacherPHID;
+  protected $attachmentMode;
+
+  protected function getConfiguration() {
+    return array(
+      self::CONFIG_COLUMN_SCHEMA => array(
+        'objectPHID' => 'phid',
+        'filePHID' => 'phid',
+        'attacherPHID' => 'phid?',
+        'attachmentMode' => 'text32',
+      ),
+      self::CONFIG_KEY_SCHEMA => array(
+        'key_object' => array(
+          'columns' => array('objectPHID', 'filePHID'),
+          'unique' => true,
+        ),
+        'key_file' => array(
+          'columns' => array('filePHID'),
+        ),
+      ),
+    ) + parent::getConfiguration();
+  }
+
+}