docs: add class, props, and attributes

Author: eddyerburgh

docs/en/api/wrapper-array/hasAttribute.md

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+# attributes()
+
+Returns `Wrapper` DOM node attribute object.
+
+- **Returns:** `{[attribute: string]: any}`
+
+- **Example:**
+
+```js
+import { mount } from 'vue-test-utils'
+import { expect } from 'chai'
+import Foo from './Foo.vue'
+
+const wrapper = mount(Foo)
+expect(wrapper.attributes().id).toBe('foo')
+```

docs/en/api/wrapper-array/hasClass.md

@@ -0,0 +1,18 @@
+# classes()
+
+Return `Wrapper` DOM node classes.
+
+Returns Array of class names.
+
+- **Returns:** `Array<{string}>`
+
+- **Example:**
+
+```js
+import { mount } from 'vue-test-utils'
+import { expect } from 'chai'
+import Foo from './Foo.vue'
+
+const wrapper = mount(Foo)
+expect(wrapper.classes()).toContain('bar')
+```

docs/en/api/wrapper-array/hasProp.md

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+# props()
+
+Return `Wrapper` `vm` props object.
+
+**Note the Wrapper must contain a Vue instance.**
+
+- **Returns:** `{[prop: string]: any}`
+
+- **Example:**
+
+```js
+import { mount } from 'vue-test-utils'
+import { expect } from 'chai'
+import Foo from './Foo.vue'
+
+const wrapper = mount(Foo, {
+  propsData: 'baz'
+})
+expect(wrapper.props().bar).toBe('baz')
+```