Extend GenerateUniqueMany with an EqualityComparer

[Mosie1]

Extend GenerateUniqueMany with an EqualityComparer to allow for case insensitive Dictionary keys.

When creating an inherited dictionary with string keys that are case insensitive, the AutoFaker sometimes tries to add duplicate keys to the dictionary. This is because the string comparison used for the generation of the keys is case sensitive.

To resolve this I added an additional IEqualityComparer parameter to the GenerateUniqueMany method and pass this parameter from the DictionaryGenerator.

[Mosie1]

@nickdodd79 Could you have a look please?