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

Reproduziere den Android-APK-Build mit flutter_webview_plugin 0.3.11 und führe den gemeldeten flutter analyze-Befehl aus. Beginne mit BrowserClient.java, FlutterWebviewPlugin.java und WebviewManager.java, in denen das Log Deprecation- und Unchecked-Warnungen zeigt. Als erledigt gilt, dass der tatsächliche Build-Fehler identifiziert und bestätigt wurde, dass der Android-APK erfolgreich erstellt wird.

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