feat(ngMock): allow override of when/expect definitions

[shahata]

Closes #5766

[mary-poppins]

Thanks for the PR! Please check the items below to help us merge this faster. See the contributing docs for more information.

• Uses the issue template (#8352)

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Thanks again for your help!

[petebacondarwin]

I like this option. It is clean, makes very little change to the codebase and is easy to understand in tests.

[petebacondarwin]

Adding to next milestone and happy to merge if @IgorMinar can LGTM it.

[IgorMinar]

otherwise lgtm

[shahata]

Cool. I added the missing example.