Add proper handling when a property’s backing field cannot be inferred or the unsafe accessor cannot be generated.

[kawasaniac]

My take on adding additional handling for the following issue: #35219

Throws InvalidOperationException with proper message as in DesignStrings (CompiledModelBackingFieldNotFound and CompiledModelUnsafeAccessorNull). Plus added additional exceptions specifically for this case.

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        Summary of the changes
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        - Detail 2

        Fixes #bugnumber

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[kawasaniac]

@dotnet-policy-service agree