More consistent syntax for cpp_type

As a side effect on my current work I recognized an interesting parser warning.

Essentially it boils down to the list<> case in these definitions taken from https://thrift.apache.org/docs/idl which (now) would cause ambiguities.

[28] MapType         ::=  'map' CppType? '<' FieldType ',' FieldType '>'
[29] SetType         ::=  'set' CppType? '<' FieldType '>'
[30] ListType        ::=  'list' '<' FieldType '>' CppType?

I wonder why we need it this way at all. Wouldn't it be better if list<> set<> and map<> would expect the same syntax?