`StructType` node update

[tanay-man]

Updated the ASR node StructType from

StructType(symbol derived_type)

to

StructType(ttype* data_member_types, ttype* member_function_types, bool is_cstruct, symbol derived_type)

[tanay-man]

I have created a wrapper function for creation of StructType. It currently only considers cstyle structs. To add function defs, we need a parameter member_functions like members in the Struct symbol. @certik @Thirumalai-Shaktivel

[tanay-man]

@Thirumalai-Shaktivel @certik , I have removed the comments.