APK Build getting failed

## System info

Issue occurs on: Android
Plugin version: 0.3.11

## Steps to Reproduce
I'm using androidx in the project and when I try to build apk,,I'm not able to build apk due to some bug in flutter_webview plugin.

## Logs

`flutter analyze`
[ +2 ms] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\BrowserClient.java:80: warning:
[deprecation] shouldOverrideUrlLoading(WebView,String) in WebViewClient has been deprecated
[ +3 ms] public boolean shouldOverrideUrlLoading(WebView view, String url) {
[ ] ^
[ ] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\BrowserClient.java:103: warning:
[deprecation] onReceivedError(WebView,int,String,String) in WebViewClient has been deprecated
[ +28 ms] public void onReceivedError(WebView view, int errorCode, String description, String failingUrl) {
[ +1 ms] ^
[ +3 ms] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\BrowserClient.java:104: warning:
[deprecation] onReceivedError(WebView,int,String,String) in WebViewClient has been deprecated
[ +2 ms] super.onReceivedError(view, errorCode, description, failingUrl);
[ ] ^
[ ] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\FlutterWebviewPlugin.java:133:
warning: [unchecked] unchecked cast
[ +1 ms] Map arguments = (Map) call.arguments;
[ +1 ms] ^
[ ] required: Map
[ +1 ms] found: Object
[ ] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\FlutterWebviewPlugin.java:134:
warning: [unchecked] unchecked conversion
[ +1 ms] List channelNames = new ArrayList();
[ +1 ms] ^
[ ] required: List
[ +1 ms] found: ArrayList
[ +20 ms] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\FlutterWebviewPlugin.java:136:
warning: [unchecked] unchecked cast
[ +12 ms] channelNames = (List) arguments.get(JS_CHANNEL_NAMES_FIELD);
[ +1 ms] ^
[ +1 ms] required: List
[ ] found: Object
[ +1 ms] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\FlutterWebviewPlugin.java:310:
warning: [deprecation] removeAllCookie() in CookieManager has been deprecated
[ +1 ms] CookieManager.getInstance().removeAllCookie();
[ +1 ms] ^
[ ] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\WebviewManager.java:193: warning:
[unchecked] unchecked conversion
[ +4 ms] mUploadMessage = uploadMsg;
[ +1 ms] ^
[ ] required: ValueCallback
[ ] found: ValueCallback
[ +1 ms] C:\src\flutter\.pub-cache\hosted\pub.dartlang.org\flutter_webview_plugin-0.3.11\android\src\main\java\com\flutter_webview_plugin\WebviewManager.java:346: warning:
[deprecation] removeAllCookie() in CookieManager has been deprecated
[ +1 ms] CookieManager.getInstance().removeAllCookie();
[ ] ^
[ +1 ms] 9 warnings

Reproduce the Android APK build with flutter_webview_plugin 0.3.11 and run the reported flutter analyze command. Start with BrowserClient.java, FlutterWebviewPlugin.java, and WebviewManager.java, where the log shows deprecation and unchecked warnings. Done means identifying the actual build failure and confirming that the Android APK builds successfully.

Scritto dal modello di indicizzazione a partire dal testo della issue.