Optimize the SqlGuid struct (#72549)

Optimize the SqlGuid struct (#72549)

* Optimize the SqlGuid struct

Optimizes the SqlGuid struct according to the idea
from #51836.

* Update SQLGuid.cs

* Apply suggestions

* Update SQLGuid.cs

* Update SQLGuid.cs

* Update ref assembly

* Update System.Data.Common.cs

* Apply suggestions

* Update SQLGuid.cs

* Update SQLGuid.cs

* Update SQLGuid.cs

* Add a comment about binary serialization

* Expand on the comment for backwards-compatible binary serialization

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Co-authored-by: Jeff Handley <jeffhandley@users.noreply.github.com>