Switch records to classes

[JoshLove-msft]

There are some usability issues that come into play with records. For instance, if a record has a primary constructor, the constructor parameter needs pascal cased parameters (as these define the properties), but the explicit constructors use camelCase. It can then be easy to miss the constructor overloads especially when explicitly naming the argument.

[JoshLove-msft]

BCL does not use records in their APIs so we should do the same.

[JoshLove-msft]

Apparently BCL does use records in some of their APIs. We should figure out what rules they use to decide when to use them.

[JoshLove-msft]

Roslyn uses records when representing an immutable data bag.
Also, is there any perf difference between records and classes?