* Pass disabled prop to FormStep in order-notes-step.js
This way we can add the disabled class to the div or fieldset rendered by FormStep.
* Add disabled class & style for disabled FormStep components
Allows us to style disabled elements that cannot have the disabled attribute (divs) the same way as disabled fieldsets are.
* Update test snapshot for FormStep
This is because we added a class to the div/fieldset element when it is disabled.
* Remove redundant selector from form-step styles
Because we now add the --disabled modifier to the class, we no longer need the disabled selector. The new class-name based selector covers both fieldsets and divs.
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