D7 Natively support the HTML5 required and aria-required FAPI properties

Problem/Motivation

HTML5 offers a "required" form element attribute for browser-native client-side validation.

Proposed resolution

Using the #required Form API attribute, add either of the following to an element:

TRUE: required="required" aria-required="true"
FALSE: [nothing]

For buttons that shouldn't require validation (like a 'Previous' button on a multi-paged form), a 'formnovalidate' attribute can be added to its #attributes property, which would output like this:

TRUE: formnovalidate="formnovalidate"
FALSE: [nothing]

Remaining tasks

Commit the patch from #1174938-93: Natively support the HTML5 required and aria-required FAPI properties → (attached)

User interface changes

HTML5 browsers will validate form elements that are marked as required, giving the user feedback on empty fields as they submit the form.

API changes

This patch adds the following options to the Form API:

$form['myelement']['#attributes']['required'] = TRUE;
$form['mysubmitbutton']['#attributes']['formnovalidate'] = TRUE;

Original report by Dave Reid

Currently adding a #required => TRUE to a form element gives it a class, but now with HTML5 we can put the 'required' as a direct attribute in the form element itself.

http://diveintohtml5.info/forms.html#required

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We're going to need a follow up issues for a required/toolbar bug.