Audience validation: remove exceptions

[iNinja]

Audience validation: Remove exceptions

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Removed exceptions thrown as part of audience validation.

Description

• Implemented new (internal momentarily) method for audience validation which replaces exception throwing with a return of the new AudienceValidationResult containing the exception information.
• Added new delegate signature for audience validation
• Added tests around all the previous cases.
• Updated ambiguous references in documentation to specify the old version of ValidateAudience.

[brentschmaltz]

How much work would it be to change IEnumberable to IList?

[brentschmaltz]

Remember this call will arrive from

TokenHandler.ValidateTokenAsync(
    string token,
    TokenValidationParameters validationParameters,
    CallContext callContext, 
    CancellationToken cancellationToken)
{
    // ...
}

[iNinja]

Updated to use IList on the new ValidateAudience method.

[FuPingFranco]

LGTM