[modos189]

On Android a file input in the WebView couldn't be used. Without a fileChooser listener, tapping it opened nothing and the page got an immediate cancel. With a listener the picker opened, but the chosen files never reached the page: the URI array was built but never passed to onReceiveValue, and content:// URIs were rewritten as file:// paths. After that the input stopped responding until the WebView was recreated. iOS isn't affected, since WKWebView shows its own picker.

The WebView now opens the system document picker (ACTION_OPEN_DOCUMENT) itself and passes the chosen content:// URIs to the page. The page gets the real name, type and content without any storage permission and without a new dependency. accept becomes the picker's MIME filter. An extension with no known type, like .gpx, shows all files instead of hiding the ones the page accepts. multiple enables multi-select. If the view is disposed while the picker is open, the page gets a cancel. The undocumented fileChooser event is removed, since it never delivered a result. A TODO marks where an app-provided picker could be plugged in later, as with the popup presenter in #29.