[tcgc] change generic decorator list data structure to support duplicate decorator use case

[tadelesh]

fix for https://github.com/Azure/typespec-azure/pull/966

[azure-sdk]

All changed packages have been documented.

• :white_check_mark: @azure-tools/typespec-client-generator-core

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### `@azure-tools/typespec-client-generator-core` - _internal_ [✏️](https://github.com/Azure/typespec-azure/edit/fix_decorator_list/.chronus/changes/fix_decorator_list-2024-5-26-13-53-0.md?pr=/Azure/typespec-azure/pull/1082) > change generic decorator list data structure to support duplicate decorator use case

[azure-sdk]

You can try these changes at https://cadlplayground.z22.web.core.windows.net/typespec-azure/prs/1082/

Check the website changes at https://tspwebsitepr.z22.web.core.windows.net/typespec-azure/prs/1082/