feat: Implement the Web Share Target API (#3230)

* Use the web share target API

* Make requested changes

* Remove line

* Add application/json back

* Add application/vnd.excalidraw+json

* Add 'POST' check back

* Make requested changes

* Update src/appState.ts

Co-authored-by: Thomas Steiner <tomac@google.com>

* Update test

* Override initializeScene

* Use Excalidraw MIME type

* Minor fixes

* More MIME type tweaks

* More permissive file open

* Be overpermissive in file open

Co-authored-by: Thomas Steiner <tomac@google.com>
Co-authored-by: tomayac <steiner.thomas@gmail.com>

public/manifest.json

@@ -26,5 +26,18 @@
       }
     }
   ],
-  "capture_links": "new_client"
+  "capture_links": "new_client",
+  "share_target": {
+    "action": "/web-share-target",
+    "method": "POST",
+    "enctype": "multipart/form-data",
+    "params": {
+      "files": [
+        {
+          "name": "file",
+          "accept": ["application/vnd.excalidraw+json", "application/json", ".excalidraw"]
+        }
+      ]
+    }
+  }
 }