Introduce a new flag to generate the _serializedAdditionalRawData as an internal property

[ArcturusZhang]

Fixes #4835

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[joseharriaga]

Hello, @ArcturusZhang. I would like to grab an alpha version of the generator with the changes in this PR and test it in the OpenAI library.

Question: My understanding is that the PR pipeline generates an alpha version that I could use for this purpose. Do you know where can I find it? Also, could I ask you to rebase this PR on top of a more recent version of CodeGen? We're currently on version 3.0.0-beta.20240628.1, so anything after that should work. 😊

[ArcturusZhang]

Hello, @ArcturusZhang. I would like to grab an alpha version of the generator with the changes in this PR and test it in the OpenAI library.

Question: My understanding is that the PR pipeline generates an alpha version that I could use for this purpose. Do you know where can I find it? Also, could I ask you to rebase this PR on top of a more recent version of CodeGen? We're currently on version 3.0.0-beta.20240628.1, so anything after that should work. 😊

Sorry I did not notice the message :(
You could find it here: https://github.com/Azure/azure-sdk-for-net/pull/44667/files#diff-93a28d9569550c68624a8ad2209a6fae1d4f88237e4b5414eed2ecac4ef8c98fR225

Since this PR has not been updated for a while, I need to update it and triggers another regen, and you could find the version number in above PR (updated in place)

[trrwilson]

Verified to achieve the intended effect for the OpenAI .NET library in this draft PR:
joseharriaga/openai-in-typespec#173

Which consumes PR resources from:
https://dev.azure.com/azure-sdk/internal/_build/results?buildId=3972319&view=artifacts&pathAsName=false&type=publishedArtifacts

[m-nash]

Be sure to verify the preview before merging. Since everything is gated behind the new flag there should be no diffs other than the version bump.