Replace Moq dependency with a different Mocking library

[bacherfl]

Due to the controversies around the Moq library (see https://github.com/moq/moq/issues/1372), we may want to consider switching to another mocking library, like e.g. NSubstitute to avoid any privacy issues.
[1] Contains an example of how this was done by another previous Moq user.

Note: Currently we are using v4.18 of Moq, and the controversial change has been introduced with v4.20 and above, so currently this repo is not directly affected by the change. However, we should not merge any renovate PRs bumping the Moq dependency

References:
[1] Afterlife-Guide/AppSettings.Merge#6

[askpt]

Is someone planning on picking it? Can look into replacing Moq with NSubstitute.

[Kavindu-Dodan]

I don't see any PRs yet, so @askpt feel free to open a PR with the change :)

[benjiro]

The following remaining tests need to be converted

Hook_Hints_May_Be_Optional
When_Error_Occurs_In_Before_Hook_Should_Return_Default_Value
When_Error_Occurs_In_After_Hook_Should_Invoke_Error_Hook

[toddbaert]

Now only:

Hook_Hints_May_Be_Optional
When_Error_Occurs_In_After_Hook_Should_Invoke_Error_Hook

remaining.