Add index on {file_managed_revisions}.uri and {file_managed}.vid

Problem/Motivation

manualcrop does the following query when file_entity_revisions is enabled:

riaDB [web]> EXPLAIN SELECT c.x, c.y, c.width, c.height FROM manualcrop c INNER JOIN file_managed_revisions f ON c.fid = f.fid WHERE c.style_name = 'foo' AND f.uri = 'public://foo/foo.png' ORDER BY c.vid DESC;
+------+-------------+-------+------+---------------+---------+---------+----------------+-------+----------------------------------------------+
| id   | select_type | table | type | possible_keys | key     | key_len | ref            | rows  | Extra                                        |
+------+-------------+-------+------+---------------+---------+---------+----------------+-------+----------------------------------------------+
|    1 | SIMPLE      | f     | ALL  | fid           | NULL    | NULL    | NULL           | 31084 | Using where; Using temporary; Using filesort |
|    1 | SIMPLE      | c     | ref  | PRIMARY       | PRIMARY | 4       | web.f.fid |     1 | Using where                                  |
+------+-------------+-------+------+---------------+---------+---------+----------------+-------+----------------------------------------------+
2 rows in set (0.00 sec)

With the patch:

MariaDB [web]> EXPLAIN SELECT c.x, c.y, c.width, c.height FROM manualcrop c INNER JOIN file_managed_revisions f ON c.fid = f.fid WHERE c.style_name = 'foo' AND f.uri = 'public://foo/foo.png' ORDER BY c.vid DESC;
+------+-------------+-------+------+---------------+---------+---------+----------------+------+--------------------------------------------------------+
| id   | select_type | table | type | possible_keys | key     | key_len | ref            | rows | Extra                                                  |
+------+-------------+-------+------+---------------+---------+---------+----------------+------+--------------------------------------------------------+
|    1 | SIMPLE      | f     | ref  | fid,uri       | uri     | 767     | const          |    3 | Using index condition; Using temporary; Using filesort |
|    1 | SIMPLE      | c     | ref  | PRIMARY       | PRIMARY | 4       | web.f.fid |    1 | Using where                                            |
+------+-------------+-------+------+---------------+---------+---------+----------------+------+--------------------------------------------------------+
2 rows in set (0.00 sec)

Proposed resolution

See patch.

Remaining tasks

User interface changes

API changes

Data model changes