refactor: send MessageForm as child prop to Disclosure component

This commit refactors the Disclosure component to receive the MessageForm component as a child prop. This avoids the need to pass the courseId and unitId props through to the Disclosure component, which does not make use of either prop. This decreases the prop drilling and only passes these props through to components that actively use them.

src/components/Disclosure/index.jsx

@@ -5,10 +5,9 @@ import { Hyperlink, Icon } from '@edx/paragon';
 import { Chat } from '@edx/paragon/icons';
 import { getConfig } from '@edx/frontend-platform/config';
 
-import MessageForm from '../MessageForm';
 import './Disclosure.scss';
 
-const Disclosure = ({ courseId, unitId }) => (
+const Disclosure = ({ children }) => (
   <div className="disclosure d-flex flex-column align-items-stretch px-4 py-3">
     <h2 className="text-light-100">
       Xpert
@@ -45,13 +44,12 @@ const Disclosure = ({ courseId, unitId }) => (
       </Hyperlink>
       .
     </p>
-    <MessageForm courseId={courseId} unitId={unitId} />
+    {children}
   </div>
 );
 
 Disclosure.propTypes = {
-  courseId: PropTypes.string.isRequired,
-  unitId: PropTypes.string.isRequired,
+  children: PropTypes.node.isRequired,
 };
 
 export default Disclosure;

src/components/Sidebar/index.jsx

@@ -83,6 +83,10 @@ const Sidebar = ({
     });
   };
 
+  const getMessageForm = () => (
+    <MessageForm courseId={courseId} shouldAutofocus unitId={unitId} />
+  );
+
   const getSidebar = () => (
     <div className="h-100 d-flex flex-column justify-content-stretch">
       <div className="d-flex flex-column align-items-center p-3">
@@ -107,7 +111,7 @@ const Sidebar = ({
           </div>
         )
       }
-      <MessageForm courseId={courseId} shouldAutofocus unitId={unitId} />
+      {getMessageForm()}
       <div className="d-flex justify-content-start">
         <Button
           className="clear mx-2 mb-2 border-0"
@@ -137,7 +141,7 @@ const Sidebar = ({
           variant="primary"
           invertColors={!disclosureAcknowledged}
         />
-        {disclosureAcknowledged ? (getSidebar()) : (<Disclosure courseId={courseId} unitId={unitId} />)}
+        {disclosureAcknowledged ? (getSidebar()) : (<Disclosure>{getMessageForm()}</Disclosure>)}
       </div>
     )
   );

src/widgets/Xpert.jsx

@@ -14,7 +14,6 @@ const Xpert = ({ courseId, contentToolsEnabled, unitId }) => {
   const setSidebarIsOpen = (isOpen) => {
     dispatch(updateSidebarIsOpen(isOpen));
   };
-
   return (
     <div>
       <ToggleXpert