[Design] Design for preview api-version and stable api-version

Service may have multiple preview api-versions and stable api-versions, and according to the Azure SDK Guideline, GAed/released SDK only contains stable api-versions https://azure.github.io/azure-sdk/general_design.html#service-api-versions

Now when we support versioning, .NET and Java need to generate [ServiceVersion in client](https://azure.github.io/azure-sdk/dotnet_introduction.html#dotnet-versioning-select-api-version). It may not be same as the list of api-versions in main.tsp, in released SDK, the `ServiceVersion` only contains stable api-versions.

we need to design preview api-version and stable api-version

1. How can we specify an api-version is preview version or GA version?
option1: we may need to define a decorator (such as @stable) to indicate the api-version is stable one, otherwise, it is preview version

2. Shall we separate preview versions and stable versions to different tsp files?
Option 1: mix preview and stable api-versions in one tsp files
we may need handle some complex scenarios which may make tsp complex.
e.g. when there are api-versions (2023-01-01-preview, 2023-03-01, 2024-01-01-preview, 2024-03-01, 2024-05-01-preview) (ordered list). There is a parameter which is add in 2024-01-01-preview (@added("2024-01-01-preview")), but in 2024-03-01 api-version it should not add this parameter, it will remove it (@removed("2024-03-01")), but the coming preview version 2024-05-01-preview is based on previous preview version, it still need this parameter, then we may need to add it back (@added("2024-05-01-preview "))
Option 2: sperate preview versions and stable versions
Define preview and stable versions in sperate tsp files, it is more clear, but it may need extra effort to migrate preview version to a stable version

Start with the Azure SDK General Design API-version guidance and the versioning behavior described for .NET and Java ServiceVersion. Compare the mixed-version examples in main.tsp with the proposed separate TypeSpec files, then document a decided way to distinguish preview and stable versions and how released SDKs should expose only stable versions.

Written by the indexing model from the issue text.