[WIP] Update the document for client generation

[lirenhe]

Note: This PR is still work in progress. Need contributors from different SDK to update the contents.

1. Fix the grammar issue and leverage tooling to update the wording for the content.
2. We need to include both snapshot of generated code and how to use generated code in the sample to provide a clear guidance.

• Update one sample to remove the deprecated code for TypeSpec and update the .NET sample code.

TODO:

• need to refresh all TypeSpec samples and sample code in client.mdx