TreeView: Performance improvements (#2523)

* Prevent focus event from bubbling to parent items

* Update scroll story

* Create violet-plants-sip.md

* Ignore lint error

* Update stress test

* Lift styles to root

* Remove unused imports

* Remove unused sx prop

* Clean up styles

* Create tidy-olives-know.md

* Update warning and prefix classnames with PRIVATE_

* Replace VisuallyHidden styled-component

* Use VisuallyHidden component for root level live region

* Update warning

* Style directory icon without styled-components

* Remove sx prop from item

* Disable chromatic on TreeView stress test

.changeset/tidy-olives-know.md

@@ -0,0 +1,5 @@
+---
+"@primer/react": patch
+---
+
+TreeView: Performance improvements

src/TreeView/TreeView.stories.tsx

@@ -606,7 +606,7 @@ export const StressTest: Story = () => {
             </TreeView.LeadingVisual>
             Directory {index}
             <TreeView.SubTree>
-              {Array.from({length: 100}).map((_, index) => (
+              {Array.from({length: 1000}).map((_, index) => (
                 <TreeView.Item key={index}>
                   <TreeView.LeadingVisual>
                     <FileIcon />
@@ -623,7 +623,6 @@ export const StressTest: Story = () => {
 }
 
 StressTest.parameters = {
-  // disables Chromatic's snapshotting on a story level
   chromatic: {disableSnapshot: true}
 }