vb.netコード
Dim request = webView2.CoreWebView2.Environment.CreateWebResourceRequest(
uri:="https://hoge.com/hoge.html",
Method:="POST",
postData:=New System.IO.MemoryStream(System.Text.Encoding.UTF8.GetBytes("test1=data1&test2=data2")),
Headers:="Content-Type: application/x-www-form-urlencoded " & vbCrLf)
webView2.CoreWebView2.NavigateWithWebResourceRequest(request)