Support spread of aliases and models

[ArcturusZhang]

Support the generation for typespec such as:

op foo(...Bar): void;

Currently our generator here just ignores the body, even if Bar is a body parameter.

I notice this issue when I synced the spread behavior changes here (that we spread the models as well)

[m-nash]

@ArcturusZhang can we get more context on what this issue is coverting

[ArcturusZhang]

@ArcturusZhang can we get more context on what this issue is coverting

I updated something in the description.