feat(cpp): add foundational C/C++ AST expression tree nodes

[Divyateja2709]

Summary

This PR adds foundational AST expression tree node implementations for the new C/C++ language support in the Sonar Cryptography Plugin.

The added nodes model core C/C++ expressions that are required for OpenSSL cryptographic API detection and future detection-engine traversal.

Added Tree Nodes

• CppLiteralTree

  • Represents string and numeric literals

  • Examples:

    • "AES-256-CBC"
    • "SHA256"
    • 2048

• CppIdentifierTree

  • Represents identifiers such as variable names, function names, and constants

  • Examples:

    • ctx
    • EVP_aes_256_cbc
    • RSA_PKCS1_PADDING

• CppMemberAccessTree

  • Represents member access expressions using -> and .

  • Examples:

    • ctx->cipher
    • params->key_len
    • config.algorithm

Purpose

These nodes provide the foundational expression-level AST representation required by the upcoming C/C++ detection engine implementation.

In particular:

• CppIdentifierTree enables function and variable name matching
• CppLiteralTree captures cryptographic constants and algorithm names
• CppMemberAccessTree supports object-type and struct-member resolution for OpenSSL APIs

This PR contains only AST data model additions and introduces no detection logic yet.