[FEATURE] Add autofocus attribute to BE login

Adding the HTML5 autofocus attribute to the
backend login box's username field.

Resolves: #49228
Releases: 6.2
Change-Id: I5a00d5ec260ade81fb83553a50358cddf95eaebb
Reviewed-on: https://review.typo3.org/21500
Reviewed-by: Eric Chavaillaz
Tested-by: Eric Chavaillaz
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe

typo3/sysext/backend/Resources/Private/Templates/login.html

@@ -31,7 +31,7 @@
 	<!-- ###LOGIN_ERROR### end -->
 	<tr class="c-username">
 		<td><label for="username" class="c-username">###LABEL_USERNAME###:</label></td>
-		<td><input type="text" id="username" name="username" value="###VALUE_USERNAME###" class="c-username" /></td>
+		<td><input type="text" id="username" name="username" value="###VALUE_USERNAME###" class="c-username" autofocus="autofocus" /></td>
 	</tr>
 	<tr class="c-password">
 		<td><label for="password" class="c-password">###LABEL_PASSWORD###:</label></td>