WithParsed(async swallows exceptions

### Some examples of the use of WithParsed / WithParsedAsync with expected behavior
```
internal static class Program
{
private static void Main(string[] args)
{
Parser.Default.ParseArguments(args).WithParsed(_ => throw new Exception());
```
=> Unhandled exception. System.Exception: Exception of type 'System.Exception' was thrown.
As Expected.

```
internal static class Program
{
private static async Task Main(string[] args)
{
await Parser.Default.ParseArguments(args).WithParsedAsync(_ => throw new Exception());
```
=> Unhandled exception. System.Exception: Exception of type 'System.Exception' was thrown.
As Expected.

```
internal static class Program
{
private static async Task Main(string[] args)
{
await Parser.Default.ParseArguments(args).WithParsedAsync(async _ =>
{
await Task.CompletedTask; //just for demonstration
throw new Exception();
});
```
=> Unhandled exception. System.Exception: Exception of type 'System.Exception' was thrown.
As Expected.

### When using WithParsed with an async expresion in a synchrone context, it swallows the exception

```
internal static class Program
{
private static void Main(string[] args)
{
Parser.Default.ParseArguments(args).WithParsed(async _ =>
{
await Task.CompletedTask; //just for demonstration
throw new Exception();
});
```
=> Process finished with exit code 0.
Should also notify about Unhandled exception.

Start at the WithParsed and WithParsedAsync entry points and reproduce the synchronous-context example using Parser.Default.ParseArguments. Compare the behavior of a synchronous callback with an async callback passed to WithParsed. Done means exceptions from the async callback are no longer silently swallowed and the behavior is covered by a regression test.

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