[RLC & Moduler] Handle the empty object type in tsp compiler

[MaryGao]

In tsp compiler we have an empty model, we need to decide on how to support this in both RLC and moduler SDK.

/**
 * Represent any structured model.(With properties)
 */
model object {}

Eventgrid has referenced this type: https://github.com/Azure/autorest.typescript/blob/main/packages/typespec-test/test/eventgrid_modular/spec/main.tsp#L62.

Also customer could define empty model and we should support them.

[MaryGao]

object is deprecated so we don't need to support and empty model is already supported in here: #1875.