[Refacror][AST] `sinfo_args` A0: Introduce `sinfo_args`

[MasterJH5574]

This PR is the kickoff action of our switch towards sinfo_args in CallNode, as discussed in #356 and tracked by #377.

• CallNode field type_args is changed to sinfo_args, with type Array<StructInfo>.
• For intrinsic ops like call_tir/call_packed, this PR keeps the sinfo_args value as the plain StructInfo generated from the static type, even if those op calls were provided with richer StructInfo at the time of creation. The API changes, creations and structure info deductions of these intrinsic ops will be left to the next PR, as the tracking issue #377. Since that PR, our APIs and structure info deductions of these ops will no longer rely on types.

cc @tqchen @Hzfengsy @slyubomirsky

[MasterJH5574]

These changes appear sound. The only change I would recommend is clarifying in the comment that we expect it to be used for calls to ExternFunc, since the other examples given (call_tir, call_builtin) are parsed as calls to Ops.

@slyubomirsky Great suggestion! Just added it, thanks.