feat(AssetBrowserModal): set initial focus to SearchBox (#5945)

## Summary

Some quick design feedback.

## Changes

1. Fix the placeholder text so it's showing up correctly.
2. Make the SearchBox take initial focus when the modal is opened.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5945-feat-AssetBrowserModal-set-initial-focus-to-SearchBox-2846d73d365081bfb3e0cde78c827d5f)
by [Unito](https://www.unito.io)

src/locales/en/main.json

@@ -1944,7 +1944,7 @@
     "connectionError": "Please check your connection and try again",
     "failedToCreateNode": "Failed to create node. Please try again or check console for details.",
     "noModelsInFolder": "No {type} available in this folder",
-    "searchAssetsPlaceholder": "Search assets...",
+    "searchAssetsPlaceholder": "Type to search...",
     "allModels": "All Models",
     "allCategory": "All {category}",
     "unknown": "Unknown",