Add support for calling the wrapped object's method

[thomaslevesque]

Currently, when using a wrapping fake like this:

var foo = A.Fake<IFoo>(o => o.Wrapping(new Foo()));

There's no way to explicitly call the method of the wrapped object. It's the default behavior, but as soon as a call is configured, this behavior is lost and there's no way to restore it. For instance, if we do this:

A.CallTo(() => foo.Bar()).Invokes(() => DoSomething());

The Bar method will return a default value, instead of the value from the wrapped object.

A possible workaround is to do something like this:

var realFoo = new Foo();
var foo = A.Fake<IFoo>(o => o.Wrapping(realFoo));
A.CallTo(() => foo.Bar()).Invokes(() => DoSomething()).ReturnsLazily(() => realFoo.Bar());

It's reasonably simple in this specific case, but if the method had arguments it would be much uglier.

A better alternative would be to introduce a new CallsWrappedMethod method:

var foo = A.Fake<IFoo>(o => o.Wrapping(new Foo()));
A.CallTo(() => foo.Bar()).Invokes(() => DoSomething()).CallsWrappedMethod();

CallsWrappedMethod would throw if the fake is not a wrapping fake, of course.

[blairconrad]

Note that this feature was previously discussed in #805 (comment) by our own @thomaslevesque and more recently by valued community member @asgerhallas in #1693.

[blairconrad]

Labelling as breaking because it will force an update to the interfaces that provide the fluent API. Optimistically putting in milestone vNext, because it's currently slated to be 6.0.0, and it would be nice to get our breaking changes in now.

[afakebot]

This change has been released as part of FakeItEasy 6.0.0-beta.1.