[FEATURE REQ][Azure.Identity] AuthenticationRecord should expose its constructor as public

[erich-wang]

Library or service name.
Azure.Identity

Is your feature request related to a problem? Please describe.
AuthenticationRecord should expose its constructor below as public:

        internal AuthenticationRecord(string username, string authority, string homeAccountId, string tenantId, string clientId)

In current Azure PowerShell, some properties in AuthenticationRecord is already persisted in context file with its own structure, so Azure.Identity should allow partners to chose their own way import/export AuthenticationRecord.

[schaabs]

As we discussed offline we won't be adding a public constructor on AuthenticationRecord to avoid obscuring the intended usage. As a workaround you can use the IdentityModelFactory if you need to construct this type. We are adding IdentityModelFactory for mocking purposes in #14769.

[pakrym]

This doesn't seem to be a mocking purpose though. Not sure if we should advertise model factories for non-test usages.