Json V2

[Yuri6037]

• Rewrite API to fix ambiguous calls on clang compilers: the new API will require explicit calls to J::Integer or J::Number instead of taking arbitary values; other APIs should not change
• Rewrite Lexer to use a forward only aproach (no more character look-ahead)
• Maybe allow Json Lexer to read from IInputStream
• Implement Json model checker/verifier
• Rewrite type check API: revert to good old enum
• Use a bpf::Variant