[Bug]: TCGC's body parameter should have serialization option

[tadelesh]

Describe the bug

See playground.

Reproduction

https://azure.github.io/typespec-azure/playground/?e=%40azure-tools%2Ftypespec-client-generator-core&c=aW1wb3J0ICJAdHlwZXNwZWMvaHR0cCI7DQp1c2luZyBIdHRwOw0KDQpAc2VydmljZQ0KbmFtZXNwYWNlIFRlc3TGHWRvYygiT3V0cHV0IG1vZGVsIHdpdGggdmlzaWJpbGl0eSBwcm9wZXJ0aWVzLiIpDQrGJVbJIE3FEHsNCiAgxk1SZXF1aXJlZCBzdHJpbmcsIGlsbHVzdHJhdOQAl2EgcmVhZG9ubMlZecVXICBAynQoTGlmZWN5Y2xlLlJlYWTFH8Q3UHJvcDrHWOUAvyAgI3N1cHByZXNz8AEKL21ldGFkYXRhLWlnbm9yZWQiICJGb3IgdGVzdCLzAK5pbnQzMvEArXF1ZXL%2FAKroAKpRxCvGIMU2xArFCeYAtsVg5wC1z3vmANFbXdF%2BY3JlYXRl33%2FHf0PFLMUhxjfsAS1bXdZ65QCV03l1cGTfecp5VcUsxSHGN%2BsA8Nh4Ym9vbNF1ZGVsZd91yXVExSzFIcY3xnXEWGVhbs11xBrEUCB0aGF0IGRvZXMgbm90IGV4aXN0IGluIGFueSBwYXlsb2FkyHNpbsV1bGXKcsUZbm9ux2kixAvkA219xGtAZ2V0DQpvcCBnZXTlAxAoQGJvZHlSb2%2FEYnB1dDrwAzEpOucDM8QoxAlv5QOD0SjEYuUAzm9wIHBvc3TSWeQDy9ZTxAjLICzIS%2BYDwskYxjbkAXboAi7EKg%3D%3D&options=%7B%7D&vs=%7B%7D

Checklist

• Follow our Code of Conduct
• Check that this issue is about the Azure libraries for typespec. For bug in the typespec language or core libraries file it in the TypeSpec repo
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• The provided reproduction is a minimal reproducible example of the bug.

[tadelesh]

Another problem is when multi part form data content type, the model has no serializationOptions.

[jhendrixMSFT]

Will this also handle multipart/mixed? Storage uses this in some of their operations.

[tadelesh]

How multipart/mixed work in SDK?