Add source as optional param to stub

[akgula]

Updating the input type of stub function to allow source property to be passed in. This change allows other TS files calling harness.stub to pass in a view source to harness.app.views.register. If source isn't passed in, stub will continue to register with a view of ''.

derby/src/test-utils/ComponentHarness.ts

Line 132 in 37e4136

this.app.views.register(arg.is, arg.source || '');