fix-binary-in-multipart-form-data

[qiaozha]

fixes #2045
Currently, we will try to treat binary bytes the same as other encoding to use stringToUint8Array and unit8ArrayToString util to convert it, which is incorrect,

For binary in RLC layer,
if it's in input model, we should generate it as string | Uint8Array | ReadableStream<Uint8Array> | NodeJS.ReadableStream,
if it's in output model, we will generate it as Uint8Array

For binary in Moular layer, current implemtation is treat it as Uint8Array regardless input or output.

Another change in this pr is that, previously, we will speculate if a bytes by default means binary data in the context of multipart/form-data request. As this is not yet decided by microsoft/typespec#2370, we will not do such assumption.

One more thing here, in the past swagger generation, because there's no way to express all those parts together in the multipart/form-data request, we have to manual build the body parameter, but in typespec, we naturally support to use model to group all parts for multipart/form-data request, we don't need this manual build body parameter step now. that's why I delete the transformMultiFormBody function in parameters transform.
If that model is defined anonymously, we will just generate a anonymously model.
If that model has a name, we will just give it a name and put it into the models.ts