Add support for Blazors <InputFile> component

[egil]

Render a component with the <InputFile> component inside requires additional set up, that bUnit should provide out of the box.

The current solution is to provide a mock of a IOptions<RemoteBrowserFileStreamOptions> and configure the JSInterop to handle the <InputFile> components JSInterop invocation. E.g.

var optionsMock = Substitute.For<IOptions<RemoteBrowserFileStreamOptions>>();
Services.AddSingleton<IOptions<RemoteBrowserFileStreamOptions>>(optionsMock);
JSInterop.SetupVoid("Blazor._internal.InputFile.init", x => true);

This will allow the component to render, but additional steps might be needed to test the "input" part of the component.

Related: #314

[egil]

This discussion post has a complete example for how to test a component that uses the InputFile component: #415

[linkdotnet]

To all who are subscribed to that topic: There will be a new nightly build coming out addressing that exact issue. From now on you can use a convenient function to setup InputFile:

// Arrange
var context = new TestContext();
var cut = context.RenderComponent<MyComponent>();
// Arrange the file which gets uploaded
var fileToUpload = InputFileContent.CreateFromText("Hello World", "MyFile.txt");

// Find the InputFile component and upload the file
cut.FindComponent<InputFile>().UploadFiles(fileToUpload);

// Assert