Consider switch to webview_flutter

[mark8044]

This is not a knock on inappwebview and I understand it was superior for what this package needed early on. But webview_flutter has significantly improved especially with use of WkWebView under the hood on iOS. For many of us we are already using webview_flutter in other parts of our apps, so it would be one less dependency. Finally, webview_flutter is official and would likely have much better long long term support down the road