Mock overwrites global factory

[enbock]

Problem: After mocking a component, other tests fail.

Reason: The Element.factory will be overwritten.

Solution: Make a copy of the factory and add a "restoreComponent" to be run in afterEach(afterAll.

Side request: Rename "mock" to "mockComponent".

Expected usage:

beforeEach(function(): void {
    mockComponent(MyComponent);
});

afterEach(function(): void {
    restoreComponent(MyComponent);
});