Use the UsageFlags from TCGC directly in our emitter

[ArcturusZhang]

Takes the emitter changes from microsoft/typespec#3842

Description

This PR updates the version of emitter, which takes the usageFlags from TCGC directly to models and enums.
This means now our code model takes whatever the usage calculated by TCGC, we no longer do any patches or appendix to the usage any more.

We have a requirement that we do not generate convenience method for PATCH until it is ready. We still maintain this behavior, but the usage is controlled by TCGC which does not know the convenience method for PATCH should be excluded.
Therefore a diagnostic warning has been added to the emitter so that if the convenience method of PATCH is NOT disabled, a warning will be reported telling you that the operation should add @convenienceAPI(false).

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