Accessibility: Fix small tree page issues
Created by: umpox
Audit issue: https://github.com/sourcegraph/sourcegraph/issues/34422
Description
Fixes a few issues reported when auditing the (post-redesign) Tree page:
- Settings button isn't reported correctly on screen readers (only reads "Image")
![image](https://user-images.githubusercontent.com/9516420/167852584-de9b4725-74d7-4e07-bc8c-52cb3f5c15cc.png)
- Batch changes summary isn't rendered as a list
![image](https://user-images.githubusercontent.com/9516420/167852637-bef704ef-1f0e-4d16-a310-b6529c097a16.png)
- Code intel summary isn't rendered as a list
![image](https://user-images.githubusercontent.com/9516420/167852712-24d04006-3dfc-4025-9bb7-cf3c339363b5.png)
Note: This page is still only enabled via a feature flag (not used in production yet)
Test plan
- Ran locally, checked for visual regressions and ensured functionality works as expected
App preview:
Check out the client app preview documentation to learn more.