refactor(MultiSelect): add typescript annotations

Convert existing propType definitions to Typescript annotations on the
MultiSelect component. This is part of a broader effort to add
Typescript annotations to components, tracked in carbon-design-system#12513.
Closes carbon-design-system#12547.

Only type annotations, no breaking feature changes

.all-contributorsrc

@@ -1013,6 +1013,15 @@
       "contributions": [
         "code"
       ]
+    },
+    {
+      "login": "awarrier99",
+      "name": "Ashvin Warrier",
+      "avatar_url": "https://avatars.githubusercontent.com/u/17476235?v=4",
+      "profile": "https://github.com/awarrier99",
+      "contributions": [
+        "code"
+      ]
     }
   ],
   "commitConvention": "none"

README.md

@@ -216,6 +216,7 @@ check out our [Contributing Guide](/.github/CONTRIBUTING.md) and our
     <td align="center"><a href="https://github.com/jpsorensen"><img src="https://avatars.githubusercontent.com/u/93107699?v=4?s=100" width="100px;" alt=""/><br /><sub><b>jpsorensen</b></sub></a><br /><a href="https://github.com/carbon-design-system/carbon/commits?author=jpsorensen" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/jkap"><img src="https://avatars.githubusercontent.com/u/224587?v=4?s=100" width="100px;" alt=""/><br /><sub><b>jae kaplan</b></sub></a><br /><a href="#infra-jkap" title="Infrastructure (Hosting, Build-Tools, etc)">🚇</a></td>
     <td align="center"><a href="https://github.com/sierrawetmore"><img src="https://avatars.githubusercontent.com/u/107062203?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Sierra Wetmore</b></sub></a><br /><a href="https://github.com/carbon-design-system/carbon/commits?author=sierrawetmore" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/awarrier99"><img src="https://avatars.githubusercontent.com/u/17476235?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ashvin Warrier</b></sub></a><br /><a href="https://github.com/carbon-design-system/carbon/commits?author=awarrier99" title="Code">💻</a></td>
   </tr>
 </table>
 

packages/react/src/components/MultiSelect/MultiSelect.stories.js

@@ -232,6 +232,7 @@ export const WithInitialSelectedItems = () => {
   return (
     <div style={{ width: 300 }}>
       <MultiSelect
+        label="Multiselect Label"
         id="carbon-multiselect-example-2"
         titleText="Multiselect title"
         helperText="This is helper text"