[3.0] fix is_explicit_nested in abi generator gen.hpp

[linh2931]

Resolve #15

is_explicit_nested determines if a type is nested. It currently just counts the number of <s and returns true if the number is greater than 1. This causes problems for types containing std::vector<char>, as std::vector<char> actually converted to bytes and should not be considered as a vector. For example, is_explicit_nested returns true for std::map<uint64_t,std::vector<char>> as a nested container and it leads to an ABI of

    "types": [
        {
            "new_type_name": "B_vector_int8_E",
            "type": "int8[]"
        }

This breaks existing users.

Change to determine nestedness semantically.

Change Description

API Changes

• API Changes

Documentation Additions

• Documentation Additions