Added repro for a bug with passing commands in markup controls

[tomasherceg]

We found a strange bug - probably caused by missing validation of delegates passed to DotVVM properties.

I've added a repro /FeatureSamples/MarkupControl/CommandAsPropertyPage but I cannot find the place where to fix it.

[exyi]

I fixed the error message, otherwise the behavior looks "fine" to me.

1. Normally, it should definitely error out, since the Click command has type Func<string, bool, Task> - i.e. it requires arguments, and the button provides none.
2. You call the command from a value binding, so it makes sense that evaluating the value binding will call the command. As far as I understand it, _control.Click.ToString() invokes the value binding, which invokes the command.

Using the value binding to call commands is definitely not recommended, commands should only be invoked from command or staticCommand bindings. staticCommand is preferred to call control properties, since it works for calling both command and staticCommands

[tomasherceg]

The ToString() workaround in the debug mode probably works because of the bug in .NET - see dotnet/runtime#96385

[tomasherceg]

I have to add tests here.

[tomasherceg]

We need to add additional checks:

1. If DotVVM property is Command/Action/Func or any delegate, we should only allow command/staticCommand bindings.
2. If DotVVM control property value is delegate, throw a reasonable exception.
3. Disable lambda conversion except for in commands: