Added methods for setting and removing attributes on Attribute objects

Two methods have been added to the Attribute class for setting and removing attributes. They are setAttribute() and removeAttribute().

setAttribute will accept the name of the attribute and its value. removeAttribute will accept only the name of the attribute to be removed.

Twig Examples

Setting

<div{{ attributes.setAttribute('id', 'foo') }}>

Setting with an array

<div{{ attributes.setAttribute('class', ['red', 'green', 'blue']) }}>

Note: It is not recommend that you use setAttribute for classes. Use addClass(). See https://www.drupal.org/node/2315471

Removing

<div{{ attributes.removeAttribute('role') }}>

Removing multiple attributes

<div{{ attributes.removeAttribute('id', 'role') }}>

PHP Examples (assuming an Attribute object already exists.)

Setting

$attribute->setAttribute('id', 'foo');

Setting with an array

$attribute->setAttribute('class', array('red', 'green', 'blue'));

Removing

$attribute->removeAttribute('role');

Removing multiple attributes

$attribute->removeAttribute('id', 'role');