Add first-class support for C# 9.0 records

[dennisdoomen]

• By default, records are compared by their members
• This can be overridden by ComparingRecordsByValue or ComparingByValue<T>
• Also improved the reporting on how types with members are compared.

Fixes #1451

[rizi]

@dennisdoomen what does CompareByMembers do and what does CompareByValue do, what's the difference between them when talking about records?
Sorry for asking but the naming is not so easy to understand if you are new to this project.

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[dennisdoomen]

@rizi see https://github.com/fluentassertions/fluentassertions/blob/release-6.0/docs/_pages/objectgraphs.md#value-types

[rizi]

@rizi see https://github.com/fluentassertions/fluentassertions/blob/release-6.0/docs/_pages/objectgraphs.md#value-types

@dennisdoomen
Thank you very much for the fast response, the docs are excellent and now the naming makes absolutely sense.
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