[FEATURE] Added autofocus attribute to textfield and textarea

The ViewHelpers f:form.textfield and f:form.textarea were lacking the
HTML5 "autofocus" attribute. It is available for button, input and
textarea. Now Fluid reflects this correctly by adding this attribute to
the initializeArguments methods for TextareaViewHelper and
TextfieldViewHelper.

Resolves: #48689
Releases: 6.2
Change-Id: I00480dc4e76b2854dc0be36d150d32c7b432d93d
Reviewed-on: https://review.typo3.org/21994
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn