bb-base: Update form-topic.php for consistency with form-reply.php

[SergeyBiryukov]

Background: #2566

In bb-base and related themes, there's a markup inconsistency between form-topic.php and form-reply.php.

In form-topic.php, the <legend> element contains only the Revision label:

<legend><?php _e( 'Revision', 'wporg-forums' ); ?></legend>
<div>
	<input name="bbp_log_topic_edit" id="bbp_log_topic_edit" type="checkbox" value="1" <?php bbp_form_topic_log_edit(); ?> />
	<label for="bbp_log_topic_edit"><?php _e( 'Keep a log of this edit:', 'wporg-forums' ); ?></label><br />
</div>

In form-reply.php, the <legend> element contains the whole input:

<legend>
	<input name="bbp_log_reply_edit" id="bbp_log_reply_edit" type="checkbox" value="1" <?php bbp_form_reply_log_edit(); ?> />
	<label for="bbp_log_reply_edit"><?php esc_html_e( 'Keep a log of this edit:', 'wporg-forums' ); ?></label><br />
</legend>

Looks like form-topic.php should be updated to use the same markup, see ​[bb5060].

[netweb]

In 5119:

bbPress.org/BuddyPress.org: Use consistent markup in form-topic.php.

Props SergeyBiryukov.
Fixes #2568.